I “used to” have a friend like this, shared my modest holiday home with her for over 30 years.
Even let her use it occasionally with friends & family for free.
Cooked meals for us because she rarely had money to eat out, occasionally fish & chips, we paid for our own.
She knew that I had to pay council tax, ground rent, club fees, water, electricity etc.
We shared the cost of petrol for years, each taking turns driving, with our own cars.
Then on our last trip a couple of years ago when I drove she complained about having to contribute half towards the petrol.
As my car wasn’t as “fuel efficient” as hers!
Needless to say, that was our last trip there together.
You try to bend over backwards to be a nice person and to do nice things for friends but then suddenly you realise what a mug you’re being taken for.
Your “friend” really is taking the piss by asking for the £20, she’s an ungrateful cow.
I’d definitely ask her if she was joking after you gifting her such a generous weekend away.