To think this is rather rude?

Yes it’s rude not to respect what someone has clearly said is start time. Those minutes before a party are usually full of last minute jobs or getting yourself ready and I hate people arriving early then wanting sorting out. Just come with everyone else and let the hosts have a space to prep.

Just reply 'well you can - but we won't be home by then!'

I think you are reading too much into it unless she has a habit of doing this. Probably just need to clarify after 5

Just reply and say yes please you can help me (with food prep table laying hoovering etc)

This. Shes probably coming on the way back from school ŕun or woek ...so you expect her to hang around outside before you deign to let her in?

I 100% agree!

Arriving 30 mins earlier is about as bad as it gets as you’re just in the rush time before the party starts.

Offering to come properly early to help out - and making sure and coats and bags etc are stashed away- is a bit better if you are happy with that.

But if you come 30 mins early it basicallg ends up that there’s no point when you and the house are actually finished and ready for guests. She’ll start messing things up before they’re even ready!

Does she want to start eating and drinking things before everyone else or something?

I would reply very clearly that it starts from 5 -
that’s invitation from 5 onwards.

I agree that even arriving on the dot is rude.

Reply with, “That’s great news, so grateful that you will be there early to help set up for the evening. No one else has offered! Can’t believe it to be honest.”

Last time someone arrived half an hour early at my house I was in the bath! Everything was ready and I'd gone to relax for ten mins. DH let them in and I had to scramble downstairs.

She is family. Why can't she come a little bit early? She might want to help set things up or avoid traffic. You made a specific point of saying that others offered help but she was to the point. Is that what has offended you? Else, it appears to be a case of making a mountain of a molehill.

If it was my SIL she would just be informing me that she'd be a little earlier, wouldn't occur to her that it could be an issue and wouldn't occur to me either!

But I guess it depends how close you are etc, wouldn't matter to us if we weren't ready/house wasn't ready or even if we weren't home, she could just let herself in. We're a very close family in that sense.

Say "excellent, I've got a list of jobs you can get stuck into".

Then give her some if she does.

She likely means I'll be there 4.30 to help in readiness for everyone arriving. It's not rude, dramatic much.

My first thought would be that maybe she had misread or made a mistake in replying. I wouldn’t assume she was trying to be rude just based on this, but you know her and I don’t so presumably there’s a reason why you’ve jumped to this conclusion?

Anyone that wasn’t raised by wolves knows surely that it is rude to be early for social engagements though surely?! Turning up on the dot for a party is such a faux pas. Basic manners. Yes someone is first obviously but not earlier than the invite, for from 5pm I’d be there for 5.10 not before.

It rather depends if they will be in and available doesn’t it.

I had someone arrive early recently for something and was all astonishment that I wasn’t in. Because when I say from 5pm it’s because prior to 5pm I’m actually busy with something else! I don’t turn up for work meetings half an hour early either.

I’m with you. I generally plan for people to start arriving about 30 min before the named start time. I mean someone is going to end up early so might as well plan for it.

Well I'm struggling to understand what is so heinous about her arriving half an hour early, but then I'm not a typical MNer

I really don’t think that it’s a big deal if she got there half hour before the party. I would assume that she’s comfortable calling in and would like to give you a hand. I personally think it’s rude to reply to tell her not to come til 5pm as sounds like she’s only trying to help

It wouldn’t bother me. It’s my family.

She's family. What's the problem with her coming at 4:30? Or 4:00? Who cares?

Just say "great really looking forward to seeing you - will be busy getting sorted and organised beforehand so please don't come before five! Hope that's ok 👍 "

Sometimes people reply in hurry during the workday, or misread things. I would just reply "Great you can make it. It's from 5pm though - we won't be home at 4.30pm I'm afraid".

This. Surely it’s not hard to just repeat the time. She might then come back and elaborate on her response, ie, she was coming to help you…

I would take that as helpful. You are hosting an event for her parents, I will be there early (to help)

Yes, possibly depending on the relationship you have with her. But do you want to call her out explicitly and possibly have a row? Or just be as firm as she was and say no, come after 5, that way she has no reasonable comeback and you avoid the row.