Would it be okay to tell a homeless person 'never mind' after I offered to buy her food and she chose some expensive ass vegan burger?
Are you changing your mind because of what she ordered?
I'm angry she chose something so expensive.
I understand you think this was an extravagant choice, but you offered to help and you should follow through on your promise.
Would you buy me food?
If you were hungry and needed it, then yes. Your offer was generous but then you took it away. Be kind to those in need and accommodate them as best you can.