Mum friend took the piss????

This. You said you paid for the caravan and she didn't offer anything towards it. You should have asked then. If you / your mum were cooking and cleaning you should have told her it's her turn etx.

Then follow through OP.
Send her a message telling her what she owes you. You have every right

to do that. In fact it’s poor of you not to. She needs to know more clearly and without any doubt, exactly where she stands.
You allowed her to get away with it last year. That sent her a clear message unfortunately. She thought she could get away with it again.
It’s wrong of you to complain loud and clear to others but not to her.

Have your say honestly from your point of view so that she can respond honestly from her point of view.

I think you have to write out all the expenses you've incurred and send your Mum and her friend a copy stating that you'd like to receive their 1/3 share by the end of this month.

Make this the last time you go on holiday with either of them.

If your mum thinks that what her friend did was fine, I'd ask your mum to pay you her friend's share of the holiday.

Your mum's friend is a cheeky fucker but your mum condones her behaviour and doesn't back you up.

Alternatively, just stop going on holiday with either of them.

I actually think your mum is the issue here, it’s her friend, and if friend is not coughing up then your mum should be paying on her behalf, if she doesn’t want to make the friend pay.

Id be mad too.
Since your mum is ok with it, the two of them should holiday without you in future.

Your mother is a key part of the problem, inviting the lazy friend, brushing off the problems. Both of them are taking you for a ride. No more holidays with either of them!

I think you should message her now with a breezy message - “Hi Rose. Now we’re all back home I’ve had a look at the food expenses for the trip. It works out that you owe £xx for your share. My bank details are ….. My credit card goes out on 7 Nov so I’ll need it before then. Thanks. “

Sounds a bit bossy that though.

Exactly. Hence me voting YABU.

Of course she should pay her own way, regardless of whether you are saving for IVF or not. I'm not sure what that has to do with it tbh, it's none of her business.

Who was doing and paying the friend's share, your dm? Because it's not fair of your dm to be fine with it and then expect YOU to pay for her friend, so I'd be annoyed at my dm as well!

A caravan holiday with your mum and her friend, that you pay for. I can’t even imagine. Why.

This

Well you deserve it. She did this the last time and you invited her again. So two people think you are a mug - the friend and your mother.
but you can only blame yourself.

YADNBU

She really is taking advantage, at the very least she should be paying for her own food contributing financially before the holiday for food, you may need to tell, for future holidays because she may not be aware.

Yes, she is taking the utter piss, but so is your mum by allowing her guest to behave like this. CF knows your mum will let it slide and that you are reluctant to start a fight with your mum. I assume your mum was paying some of the costs, so her friend was also her guest, so you didn't want to start a row with her by throwing friend out on her ear and allowing her to make her own way home? But you need to tell your Mum that you do not appreciate being treated like an atm and a maid by her mates and you are NEVER holidaying with her ever again, no matter what she promises.

What a strange dynamic! Why isn’t your mum being more assertive with her cheeky fucker friend? Your mum doesn’t owe this woman money does she?

YABU for going away with her again tbh OP. You have already experienced this.

Next time you either don't invite her or you ask for a chunk of change upfront before booking.

Tell your Mum how unhappy you are with her friends behaviour and she (the friend) will not be invited again.

In the end, I actually had to demand that she paid for the fish and chips takeaway

How did that conversation go exactly?

Your mother is taking the piss too. She should not allow her friend to treat you like that. If she chooses to put up with it, she shouldn’t inflict her on you.
Don’t let your mother invite her anywhere with you again, mother can like it or lump it

SIL1 did this in 1999. Never, ever again. I don't have her stay with us when she visits. Lazy, entitled mare.

But why was this friend eating into your IVF fund? Surely if someone was paying for her it was your mum?

If you kept on buying things you couldn't afford you should've said to her it's her turn to get something. She's clearly tight but she didn't have a gun to your head. But maybe your mum should also have said something before?

Did your mum think she was taking the piss? Why do you keep going on holiday with someone who you feel never ever pays their way?

So no food for her then? Why so passive, it’s ridiculous.

I think you have a mum problem

The other woman is her friend?

Why are you inviting her at all?