Lease agreements and drugs

So, a while ago my girlfriend's psycho roommate flipped out and moved out of their apartment because we wanted to have an ex party. She's taken ex plenty of times but has just recently become "principled" now that she is engaged to a good mormon boy, and thinks we're all evil druggies. Anyway, she moved out with about 4 months left on their lease.
They both signed the *same* lease, and after talking to the apartment complex, it will reflect on my girlfriend's credit if her roommate decides not to pay; ie, they are both responsible for the ENTIRE rent payment, not just their portion. The apartment complex doesn't care who pays how much, just as long as they get the full payment.
The psycho roommate says she isn't going to pay her portion of the rent because she isn't living there anymore. However, her name IS on the lease, so isn't she legally obligated to pay? My girlfriend can't afford to foot their entire rent payment so we are basically left with no alternative but small claims court, right?
If she says in court she moved out because her roommate was doing drugs (which I KNOW she will say), that has no legal bearing on the lease, right? She has no evidence whatsoever about our drug usage anyway. Just want to make sure that she has no way to wriggle out of this one before we sue the hell out of her.
Thanks for any help,
phys-ex
PS: We are in Tempe, AZ if that makes any difference.

thats a really shitty situation youre in, im sure dr gonzo or one of the other handy BL law mods can help you out, but i read that you live in tempe, and i jsut wanted to say whats up because i spend 1/2 my life there so i hope things work out, but as far as i know, everyone on the lease is responsible for whatever happens, esp. if the lease is broken. but no one can *force* her to pay, so youll really just have to see what to do next! good luck sweetie!

Psycho roommate? If it's half and half then she has a say in what goes on in the apartment. By you not respecting her say, YOU are putting yourself into this predicament. You want to sue the hell out of her, because she has had a change of heart? Yes it will have baring on the case. You are basically telling her she has to agree to allow an illegal act that is going to happen at her place of residents. If it was that big of a deal with her, why didn't you have it somewhere else?

Actually, we DID have it somewhere else. No one forced her to move out. Try giving me some actual legal advice, not your moral bullshit.

As a general rule; your roomate must cover his/her portion or share of the lease payment, even if he/she moves out. This matter is complicated with the issue of drug usage. I don't think that you want to go into court and argue that she cannot leave because she now opposes your usage.
But, if you were to sue her for the unpaid portion of the lease (which she signed), I think you would be successful.
Good luck.

This is a tough one, on one hand both parties are jointly and severally liable for the entire portion of the rent due. Meaning the apartemnt complex could sue either or both for back rent or breach of contract. But, the remedies between the renters themselves gets muddy. You can't sue her for half the rent, until you pay the entire portion or the apartment complex sues you, because you lack standing, your only remedy is indemnity you can't sue on the contract because you're not in privity with the roomate.
What all that complicated legal stuff means is, you can't sue to force her to pay until you've been forced to pay your half and hers, or sued by the apartment complex. If you do pay, then you can sue her, the alleged drug use is unlikely to change the outcome, she can argue impossibility of performance, but I doubt it's going to excuse payment since the alleged drug party never happened. Simply because she disaproves of illegal activity doesn't excuse her duty to perform under the contract with the complex.
As a practical matter, I'd let this one go and try and find another roomate, bringing this into court is going to be messy. But if you decide you must, the law is mostly on your side, the only thing is you might get an ultra conservative judge who'll make a finding that the drug use made it impossible to perform. It's unlikely, but it could happen.

Did you go half's on the security deposit?
If you did they you get to keep her half.
-buzzy

Sounds like the moral (no pun intended) here is to have roomates sign contracts with each other. That way if one moves out, they are responsible for their share. I so often hear of "My roomate fucked me over" etc. They move out, you sue. Badda-bing badda-boom, breach of contract. Pay up.
Dr Gonzo, am I right?

Thanks for your replies everyone, Dr Gonzo especially. It looks like the two remaining roommates will move to a smaller apt next month, and the girl who moved out will only owe them 2 months worth of payment. We're going to just pay it now, and write her a letter stating she has until the end of the lease period to pay her share, or else it's going to small claims. If it comes to that, we simply deny ever having/thinking of having a "drug party." I think that's pretty reasonable.
The ironic thing is that this psycho ex-roommate has rolled with us several times before and usually is the "worst" of all of us--trying to get on everyone at the party, begging for other drugs, etc. Now she is threating my girlfriend that she will tell my gf's parents about the drugs (they don't know) if we try to sue her. The sheer audacity of her actions is beyond me, especially considering we have done nothing to harm her, and even relocated our party at her request. Grr.