Who is responsible for security deposits when 1 roommate moves out and the other stays?

I rented an apartment with a roommate and put down a security deposit. When the lease expired, I moved out and a new person moved in with my old roommate.
I requested the new person pay me my share of the security deposit, but she refused to. I let the issue slide, assuming I would get the deposit back when they moved out.
My old roommate and this new person have now moved out, and the security deposit has been forfeited due to damage.
What legal recourse do I have?