Hello OP,
I don't think the issue is the soup and the heating. I think the issue is that you were guilted into agreeing to this when you didn't want to, and as a result anything she does probably feels like salt on a raw wound. However, I think it would be unfair to take it out on her - she may not even know to what extent you were pressured into this.
I think you need to communicate with her, absolutely, but try and keep your resentment to a minimum because it'll make things needlessly awkward and she isn't the one you should resent, you should resent whoever pressured you.
I understand you're not in a good position financially yourself, but I really couldn't find it in me to refuse a family member basics like soup, bread, pasta...
Taking the homemade meals wasn't on, but she may simply not realize what a position you're in.
You say you allotted her a cupboard but it sounds like she can't afford to buy anything to put in it ?
As for the heating, that wasn't on either, but I think how cold your place is would be relevant in deciding how unreasonable she was - presumably you work all day in an adequately heated space, if she has to spend her days in a 10°C house I can understand the temptation to bring it up a bit for a while.
By all means talk to her, try and be very nice about it. Do tell her that you truly can't afford it - as in you have zero savings to allocate to this.
If nothing changes after that talk, THEN we'll have moved from thoughtlessness to simple rudeness and at that point it'd be okay to tell her it's not working for you and she'll need to find another place by (give her a couple of days to find another place).