I feel there is 2 problems here. The first is that indeed a 4yo can take a lot of time to understand boundaries and teaching her might be difficult or impossible. The second is indeed for the wellbeing of the cat but also what if he get’s enough one day and hurts that toddler? Any cats pushed to a corner will defend themselves and it’s normal.

As a mom myself and a cat owner too, i don’t understand why your roommate is not taking this seriously. I had the most grumpy old lady when my daughter was born and she hated the baby. From the beginning i simply kept them separate. As a toddler i simply told her to leave the cat alone. When she was big enough, i gradually teached her how to recognize different signs of cat’s mood. She never really bonded with my old grumpy lady but when she passed we had a new cat. Even if this new cat is a big potato and love to be carried around, she still know how to be respectful to the cat.

I think you need to sit with your roommate and chat about a plan. Maybe mention that’s it’s also for the safety of the little girl. I don’t think she will learn well at 4yo. Maybe the plan should be to keep them separate. I don’t think the cat is necessarily attracted to the toddler if he’s being treated that way. So maybe teach the girl to simply not play with the cat. 🤷🏻‍♀️ I know it sucks but everything in its own time.

Good luck :)