My sister is such a cow!!

Or possibly she sees it as you showing off again and making it a competition?
Look at me, I am the wonderful daughter who has sorted out the special present that mummy will love the best.

I wouldn't waste your breath with her. It'll only ruin your day with your mum. You tried and she rejected. Can't do much more.

What a shame your sister is making this a competition.

Lol. It sounds like it is OP that is making it into a competition talking about her present being the most meaningful and making up a whole to drama in her head about her sister being jealous. Her sister has simply said she has sorted her own present without any drama.

You’re not actually listening to your sister. She doesn’t want to participate in your gift, she has her own for your mother. With respect I’m sure your mother is aware of the kind of relationship you have with your sister. You don’t have to make anything unnoticeable, your sister can explain if the question is asked, you don’t need to say anything other than she arranged her own gift.

I have a sibling who won't be told to do anything, on principle. And even if asked nicely, usually says "No" if they don't fancy it.

It's definitely a sibling dynamic. They don't have to impress you or keep you sweet because you'll always be their sister / brother.

There are people on MN who really just look for the worst in everything. I often wonder if they are as miserable in real life.

Goodness. What a reaction. This is just a scrapbook for a mum. What’s a ‘jolly hockey sticks joint project‘?

MN is where fun and joy are sucked out of the most ordinary things!

What an unpleasant comment. The way people post on MN amazes me. Why would the OP have form for badgering people to make herself look good?? Narcissistic? What’s wrong with some people.

Anyway OP. Your sister is jealous of you and wants to sabotage the gift. It would take seconds for her to email a short message. Your mum will miss a comment from your sister and that’s sad but there is nothing you can do. It’s a lovely idea and I am sure your mum will adore it. What a shame your sister is making this a competition.

You’ve asked her, she’s declined giving her reasons, move on.

They all get on well, the thread title is my sister is a cow….. 🤔

I think four requests is badgering…

Why are you going on holiday with your sister when you clearly do not like each other?

Did you ask all the siblings if they wanted to do this before you decided to? I ask because as PP have pointed out, there could be many reasons your DS doesn’t want to participate. You remind me a lot of one of my DS - we all love our parents, no backstory or anything but she always assumes we want to celebrate them or contribute to stuff for them without consulting. And she often wants to do things that reflect her budget, tastes, and relationship with them which are different from the other siblings. She is your mother's daughter too - let her celebrate her in a way that she’s happy with. And agree - you seem to be centering yourself here. You’ve decided it’s a great gift. You’ve assumed the only reason she would decline is because she is threatened or jealous of you. Let her do her own gift and crack on with yours, it’s not that deep.

Your sister hasn’t made something similar as a gift, has she?

I have two sisters and I would have definitely suggested the idea as a joint gift and doing it together.

Does she "do photos" in general?

I wouldn't have anything to send.
I just don't take photos of people in general, including not taking photos of myself and my partner.

If someone in family tried to push it and babbled about "just five minutes" and "ruining their idea", I would think they are the cow in the room.

You know for certain that she is trying to undermine you and sink your idea. Yet you have gone back to her 4 times already, prompting her, trying to get her to change her mind and now want advice on how to word yet another message to her, saying that she has missed the point.

It would be better if you left it alone now OP otherwise it’s you who looks like the controlling baddie in this situation. It will be you who looks like the one missing the point. Your sister has stated she doesn’t have time and has already sorted her gift. You must accept that and stop antagonising her. She probably feels harassed by you and your project already.
You are in danger of now taking it too far and using the memory album as a weapon to highlight her refusal of your invitation to take part which she is perfectly entitled to do. Just do the best you can and minimise the absence of her contribution. You sound very experienced in producing nice mementoes like this so shouldn’t have a problem covering for her. It’s simply about ensuring you are not hurting your mum with your otherwise very thoughtful gift.

AIBU in thinking she’s a complete cow??
You can think whatever you like of course.
But you would be very unreasonable to highlight your negative thoughts about her in any way to your mum.
From what you have written, I do feel your OP title isn’t justified. Your sister is just a different sort of person to you.

I have the same experience here. I was treated very differently to my sister growing up, and she has NO idea about it. She left for university, and my life was awful. She idolises my mum and won't hear a single word against her.

We've just had a family celebration for my mum - my sister wanted speeches, photographs etc. I found it very, very difficult.

It's a nice idea OP, but your deciding to do something doesn't make it compulsory for other people to participate.

Having been through a hard place where I honestly wouldn't have had the mental space to do this in a timely fashion, I say just take that she doesn't have time at face value and continue with your project by yourself. She has her own ideas.

Yup - you forgot. You told me to keep my opinions to myself, but the OP clearly asked for those opinions to be shared. The alternative, if you are saying you didn't forget, is that you are the kind of person who thinks that people should either agree with you or shut up. Which is a very unfortunate personality trait. If you think that people shouldn't share negative opinions on a page that is clearly titled "am I being unreasonable" then you don't really understand the point of the forum.

Fair enough. I mean it’s just a photo book not a year long documentary but ok.

Have you not read the other posts? Including OP's admission that she's tried to force these "joint projects" on her relatives before, again without actually consulting anyone to see if it was something they'd actually want to do? Assuming that people will like the same things you like is not a pleasant personality trait. You may think a photo memory book is lovely idea, but for many other people they'd find such a thing utterly noxious - particularly if they already have the same photos. Or don't have pleasant memories of family times. Which is the case for a lot of people. As such being part of a project that involves looking back over old photos could be incredibly unpleasant. They may get on with a parent now, but it could have taken them a lot of hard work and therapy to be able to do that. Or they might like their mum but really find their siblings utterly insufferable. The point being: forcing your "happy families" viewpoint on others isn't terribly helpful.

I do always wonder why people expect OPs to stay beautifully calm, thoughtful and kind, when they’re getting quite aggressive responses? I mean we’re not talking about the thoughtful ‘perhaps your sister might have other reasons’ posts, we’re talking about the ones suggesting OP is thoughtless, looking for glory or diagnosing her as a narcissist. But - each to their own with acceptable boundaries.

No, not forgetting. Just like you said, different opinions.

@Threepiece saying nothing at all is showing your child they do not need to set boundaries and to be honest the OP sounds more and more up her own arse as she posts. Her sister said no. OP cannot compute somebody saying no to her. As I said in my other post not all kids have the same parents even if it is the same human. My mother abused me, loved my sister and my sister would do this photoshite too. Not everyone needs to be nor should be a 'yes' person to appease others. OP comes across as the golden child of a narcissistic parent and her sister the scapegoat and if that is the case, and it was with me, then no way would I be considering wasting my time trying to fill in a memory book on behalf of the other sibling who wants to make it.