<human>: Can you give me the gist of the text in a nutshell?

My sister, we'll call her K, got an apartment with her best friend L and another person, J. Things were great until about 8 months in when J disappeared. He left some stuff at the place but never came home and didn't help with bills. His room was subletted to a random person that could pay the rent(she ended up screwing them over by not paying, stealing their stuff, and vanishing.) On the last month of the lease, they simply couldn't make rent and got evicted. Best friend relationship was ruined, none of the 3 roommates talk to each other now. It is about 6 months later and K gets a bill in the mail from collections for $2,251 for unreturned key cards, late fees, damages, etc. My poor sister is pretty naive(obvious by going into the lease with a couple of irresponsible people) and feels that she is stuck with this bill all on her own. I know that all three people were on the lease but I am afraid that if she starts to pay up, the company will quit trying to collect from her former roommates. Is there anything she can do to be sure they have to pitch in to clear the debt?
<bot>: Sister got screwed over by bad roommates, any ideas on how she can get them to pay their share of the $2,251 debt?