I think this is easily explained. Over a period of time, her gratitude has sometimes bordered on shame for feeling like, in her words, "a charity case". You can add to that her fear and dread of you telling the others about how much you have helped her. A little paranoid voice sometimes goads her, convincing her that surely nobody could be as seemingly altruistic as you appear to have been - snipping away at her loss of self esteem due to feeling like a desperate, poor relation. Yes, she has been incredibly grateful, but it has also (completely unintentionally) undermined her self-confidence. She wishes she could have said no, but she really needed the help.
Sometimes, we can be afflicted by a very strange syndrome, a kind of, "reverse pschology" . Basically, in with the genuine need for financial help, she has also felt envious, embarrassed and shamefaced. Her gratitude has been soured by suspicion of your motives, whilst at the same time feeling very humbled by your obvious superior financial position.
It's been churning up inside: shame, guilt, desperate gratitude, all of that - which she has projected back at you, convinced you can't be such a saint and must have ratted her out to the friendship group. Out it's all come, like a stream of psychological vomit, the little voice pushing to the front in a drunken moment of savage spite and misplaced hurt. Once drunk, she's convinced herself that you're a two faced cow as she slurs out her accusations. "Ha, I'm on to you!" she thought, as she knocked back her sixth gin and tonic.
Only she wasn't. And all her shame at feeling poor and needy has wanged straight back in her face, knocking her on her arse in front of everyone and leaving her feeling like a complete bitch. If she thought she didn't deserve a friend like you before, she's convinced of it, now. And it hurts like crazy, that feeling of not being as good, or as well off, or as in control as everyone else.
She will be either defensively defiant, or a cringing, mortified wreck right now. If she has any sense of self worth left, she'll be desperately trying to shine it up, is my guess.
Go to see her, get it all out in the air. I am convinced she is feeling utterly dreadful right now.
Question is, can you fix it? Good luck, OP. I would love to know how it goes. Xx