Old roommate wants to move back in with me, but I fear my schooling being screwed over.

One of my best friends and I (along with another girl) (24-25F) lived together throughout 2021-22 before the 3 of us all parted ways last may. My BF was the one to trigger the idea of us all seperating as she wanted to move in with her boyfriend, mind you she gave us **7 months** notice so we could finish up our lease.

A few months later she comes to me saying that she’s miserable with her boyfriend and is considering wanting to move back in with me when my own lease is up (at the beginning of may). The thing is, I don’t know if I can trust her not to cause issues with my situation.

You see, I am currently trying to get into a particular university program for the fall of 2023 that is very demanding (7 classes at once, all year) and would plague me with 7 exams worth 70% of my final mark each. These exams would be right around where our lease would be up, and so if shes wanting to part ways again, then that would be a massive inconvenience for me.

The last 5 years she has not lived somewhere for longer than a year, and has literally jumped from our old living arrangement into a new one that she is unhappy with barely 3 months into living in. Even though she promised me she would not date for a long time (if she does break up with her boyfriend) and ergo would stay in one spot (since her bills are too high for her to be able to afford her own apartment), I just dont know if I can take her word for it. We got along and everything while living together (the other girl caused 90% of the problems), but even so it’s concerning. She told me she doesnt know what she wants to do with her life, whether it be staying here to go to school, moving to a different province or taking up a job that involves lots of travelling.

I am looking for stability whilst entering what could be the most stressful period of my life and I dont know if she could provide me with that. I can make it work if I lived on my own instead (albeit Id have to take out more student loans to make up for my hours at work being cut), but having a roommate would just be easier. I tried talking to her about it, and she said shed make sure I would have somewhere to go/would be ok if we parted ways, but even so if im studying for 7 exams at the same time then ill have NO time to clean the whole apartment and look for a new place to live, or look for a new roommate.

*tl;dr: old roommate with history of jumping living arrangements, as well as uncertainty about what she wants to do with her life, wants to move back in with me as I am about to enter a demanding university program. Chance of being screwed over is on mind as final exams will be around the end of the lease we would be on.*

Would it be unreasonable of me to tell her that if we live together, and she wants to leave, that she will have to do ALL the cleaning and be responsible for finding me a new place/roommate I approve of? Or if we were to sublet after my exam period she would pay the $75 sublet fee (canada)? Or should I go about a different way of dealing with this?

Edit: spelling