To think this is unfair? Holiday.

@Chefpig just because there will be an atmosphere if you don’t let her have her way is not a reason to give in to her. Worst case then is you stay away in your quiet caravan nearer the beach.

So you either say “no, my turn to choose as agreed” or you just give in to her. Either way, make this the last holiday where one of you books both sets of accommodation. Book separately.

Op is paying not her mum. If you've paid op you must be the lead name on the booking? Take the one you want she can't stop you.

Please put your foot down. When asked about regrets the only one I have is being utter people pleaser aka doormat in my youth.

So basically you have 2 caravans and you both want the better situated one. You had previously agreed that it's your turn for first choice this time, but now your mum is going back on that, under the faux-concern that the less nice one is better for your dogs. Honestly, a parent that would do that to their own child isn't someone I would go away with.

I think the other person being your mother is quite important information.

I would insist my mum take the nicer accommodation, especially if she's paid for it.

Frankly, I wouldn’t want someone else’s pets in my accommodation. If they put their pets in it, then that’s what they are taking! Maybe don’t put the dogs in any caravan until sorted out which one is yours, otherwise YABU.

For my mother, I'd probably just put up with the less nice accommodation and accept that it is a bit ungenerous (given that it is your turn to have the better accommodation) of her but as she is paying this time, I would just suck it up. Obviously as it is your mother, there will be a whole host of other stuff in the mix here too. Otherwise, you'll just feel hacked off and might as well not go or she will feel hacked off and thinking she might have well have not gone. What do you think would happen if you said you wouldn't go? In future, I'd maybe re-think these trips away - maybe try a day out instead?

@Chefpig Why are you being awkward with us? If you start a thread on here, it's not unreasonable to expect you to engage with people who comment. In fact, not to do so is actually rude. We can't be of any help if you won't answer questions, which means we don't understand the situation enough to comment.
I'll try again but I'm not hopeful! @Chefpig , what sort of place is the accommodation?
Why are there separate book in times?
Who made the booking?
Why do you not know already which room is "best"?
Why are you holidaying with this friend if your relationship is as shaky as you imply?

Frankly, I wouldn’t want someone else’s pets in my accommodation. If they put their pets in it, then that’s what they are taking! Maybe don’t put the dogs in any caravan until sorted out which one is yours, otherwise YABU.

Hopefully this will be the last time you agree to go on holiday with this person.

Honestly? So much angst for what should be a nice break away!

Does the caravan position really matter that much?

I'd just take whatever caravan and be glad to be getting away. I'd let mum have the nicer position caravan because she's my mum, and I'd really not care about this

If you are worried the whole break will be made about the caravan nonsense, just say now you don't want to go. Sounds like the whole thing has potential to be miserable if you all make such a big deal about who gets which same grade caravan on the same site

Sounds like she was happy for you to have the choice of caravan when she thought they were the same (an empty gesture) but as soon as she realised one was much better, she changed her mind. She sounds very selfish. Next time you book and pay, get her a tent and yourself a deluxe caravan

Honestly such a storm in a teacup. So both caravans are the same inside but one is better situated.
If it matters that much to you why not ring up the site and ask which one is going to be available for early check in and take it from there. To be fair to your DM if it does take a lot of time to get the dogs settled and you’re unable to go out whilst you’re doing that, then it makes a lot of sense for you to take the first available caravan.

She’s paying so surely it’s her choice?

But if you’re desperate for the other caravan, then just put your foot down and say that one will be better for the dogs etc so you’re having it as that was what was planned - but as she’s paying for it there’s not a lot you can do.

Are you not planning on spending time together?
Surely it doesn’t really matter which one has which as you’ll both be in each others anyway?

Are you planning on walking to the beach without her?

Just don't go then. Stay at home and have a lovely peaceful time with your dogs!

It should be turn about.
But why are you booking holiday accommodation with big discrepancies in the standard?
if we go away with others we either each book our own room or if it’s sharing an Airbnb we make sure we get somewhere with bedrooms a similar standards

Well I agree with others that your whole post doesn't make any sense. But to answer the specific point here ... just don't argue with her. You say:
"You had first pick last time and we agreed that I would have first pick this time, so that's what's going to happen"
Don't get drawn into an argument, just keep repeating that sentence.

But WHY is there a "first one"?

If you're this bloody obtuse with your friend I'm not surprised she's being awkward.

Why are you going on holiday with someone you clearly hate ?
How do you know that there will be discrepancies in the room conditions this time? Usually when you book 2 hotel rooms they’re very similar.

Never mind the rooms and the pets, she sounds awful.
Why are you going on holiday her? It sounds like a personality type so surely you must know this about her already.

What do you mean the first one?

Are they paying more money than you?

Most places have similar rooms for similar costs, so I’m confused as to how one accommodation is way nicer than the other.

And who booked it?
Surely you get the accommodation you booked and she gets the accommodation she booked - you can’t just chop and change it.