^ what she said and what was said above. If it goes to collections, it goes on her credit and that's not pretty. And a lot of leases can be broken but for a fee. It's usually a fee of a couple months rent or something but worth it to save your credit.

If they both stop paying... what will the other girl do? Get new roommates? Pay it herself? It only gets ugly if it's not paid at all, they don't care who the check comes from.