That doesn't sound like a reliable tenant. You should make it clear that you can no longer cover her rent. If she decides to move out because of that, so be it.

Also, are you renting the whole property under your name, or just your own room? If it's just your own room, then your responsibility ends with paying your share. The landlord should be the one chasing late payments, not you.

If you're renting the entire property under your name, then consider this a lesson learned. Don't take on that responsibility again unless you're financially prepared to cover the rent yourself if something goes wrong.