Hhhhm. You might try and threaten to notify the landlord that her cats are causing a lot of property damage to the rental, as leverage to get her to take more responsibility.

However, a landlord's priority is always going to be their property and their money. If you actually notify your landlord, there's a pretty high chance your landlord would deduct both of your security deposits. If they're really pissed (haha) about the cats, they may try and evict you both, but eviction is a very lengthy process. Canadian cities tend to be tenant-friendly when it comes to the risk of someone getting stuck on the streets during the winter. More likely, your landlord may just decline to renew your lease.

You might try and take her to small claims, if you have receipts for everything her cats have ruined. IANAL, consider posting in /r/legaladvice?

Other than that, perhaps pay someone to fix/replace your door and get a sturdy lock with a key, so neither the cats nor your roommate can continue accessing your room.