Grown womenseething at each other in Costa is not a good look, and is bad for your soul.
Read back over the exchange.
Hindsight makes everything easy, but you were doing so well when you said 'I thought you were getting them because of the £8 you we me'. and when she said 'fine, I'll use my card' you should have said "OK, thanks, I'll have a coffee and that cake"
You were passive aggressive in saying you would get your own at that ppint. She owed you, you made the point - accept it!
And then you could have said 'look, this constant paying for things on your behalf creates these kind of complications - and to be honest it often feels as if I never quite get back what I spent. So to keep things calm and straightforward, best we do our own paying for stuff"
Do not engage in any passive aggressive come-back.
If it gets raised again, be honest and direct. Tell her that you don't want to row, you don't want to stop meeting for coffee, but you do need to stop paying for her stuff.
If she asks you to order anything in future, say 'sure - as soon as you ping me the money, I'll order it straight away'.
Be honest and direct - before it develops into a bitching match.