Security Deposits: Lazy Roommate Trying to Take Security Deposit I Worked for

My question involves landlord-tenant law in the State of: California

Last year me and another roommate moved into an apartment with a 1 year lease and we each paid $275 of the $550 security deposit. At the end of our lease (September 2011) I asked my roommate if she could help me clean the apartment before taking off and she didn't. She simply came in, vacuumed her room and left. My mom (who was 6 months pregnant) and I were up from 8 am to 5 pm cleaning and scrubbing the unit and making sure everything was in great condition before leaving.
Anyway, 3 weeks later we get our security deposit back which stated that instead of getting any money back, we owed $6 after all repairs. I was shocked because the apartment was spotless when we left! So I called my roommate and told her about the charges but she didn't seem to care much. I told her I was going to fight the charge and try to get the money back and she said good luck. I worked for 2 very frustrating months (making calls, writing letters, leaving messages) and finally the company agreed to give me $263. This entire time, my roommate didn't do a single thing to get our money back. I asked her to make a call several times and she always gave an excuse as to why she didn't ("I was planning a birthday party," "I was babysitting," "my mom was busy," etc.) So finally I told her that after all my work I was only able to get $263. I also told her that from the $550 we rightfully paid $62 for our final water&power bill and $20 for a drip pan that was messed up, meaning we were each owed $234 so from the $263 I would give her $30 back. I told her that I worked hard to get back the entire amount but if they agreed to give me half, then that should belong to me because I tried for so long to get it. Basically if I hadn't called and fought for the money, we would still be owing $6 to the company. I think this is pretty fair because instead of owing the company money she is getting $30 back without having to lift a finger.
So the letter sent to me by the management company states the amount they are willing to refund and it says each tenant must sign the paper. I asked her if she wanted to keep fighting the other half of the charges, which would give her back her half of the deposit, then she could. Otherwise, I asked, if she could please sign the paper because I really needed (and still need) the money I was able to get. She said that she would not sign the paper because I owed her half of the money I was being given by the company. I was in total shock. She didn't do a single thing, she didn't even care about getting the money back until after they gave me an offer. I told her I was keeping the money I was owed ($234) and giving her the rest so it's not like I was keeping money that wasn't mine.
Anywho, now she refuses to sign the paper completely until we get our full refund of $550 yet she isn't willing to fight for it. So I am kind of stuck because without her signature I get no money, and I am the one that has to deal with the company again if I want her to sign. I am a student in a UC, I live off campus, I work two jobs, but I still need money for books and completion of rent. My roommate dropped out of school, moved back home, doesn't work, doesn't pay rent or bills or food or gas, and I don't think it fair for her to take even a third of the money that wouldn't even be here if it weren't for me. What can I do??