Its an unfortunate situation, but she really is taking advantage of your friendship.
If you cant say NO, as I would, then you do need to be a bit more assertive and stick up for yourself because she is abusing your friendship and manipulating you. Now that she knows it works, she will continue to walk over you and essentially you will be paying for her to be your friend. Real friends dont do this.
As a compromise:
1. Contact or get the details from the Uni about Bursaries and hardship funds. Print them off and give them to her to complete. the SU normally have the ability to probide short term loans.
2. If she has debt troubles, then she should address them by talking to someone like Stepchange or CAB to work out a budget and deal with any creditors.
3. If its just for the period of the exams, then cook in bulk i.e stews and soup, porridge for breakfast and shop cheaply at places like Aldi, netto , Lidl etc.She cna eat well for less and if you cook, then she cna either eat it or not, but it limys her excuses to ask for more money from you.
I might consider carrying her for a few weeks, but tbh she has to take responsibilty for herself and needs o give you a clear plan of what she intends to do, now or immediately after the exams. If she wont help herself you cnat trust her and she will continue to walk over you. If it becomes a problem for her, then you should get new friends next year.