Put up some ads and try to rent it. You have a so-so chance of getting rid of it for Oct 1st.
If you don't or you need to reduce the rent on the unit, then you gotta go after her.
Start playing nice with her right now....tell her you are going to try and rent it. Tell her that you are going to return the security deposit (because, if you DO rent it...you need to give it back to her within 15 days or she has the right to double it back - you need to file with the RTB to keep a deposit in any situation UNLESS the tenant gives you written permission to keep it). But, like I said, tell her you are going to give it back to her if you can rent it (even if you are not) and get a forwarding address. Tell her she can use a friend...family...anything....just get a damn address. Tell her, you also need to forward her mail, etc. Just get the damn address. Play nice, blah blah blah, then fuck her.
Also, if she filled out an application and gave work info, family info, school info, etc...you can track her down that way. You can also perform another credit check to get her address.
So, like I said...try and rent it...reduce the rent if you have to (it reflects well on you during an arbitration case to show that you made an effort to re-rent the property).
Like Grid said, she has signed a contract guaranteeing the rental unit will produce x amount of dollars for 11 months.
IF you do rent the unit for the same price for Oct 1st and there is not loss of rental revenue there is little that you can do. Technically, unless she has signed a liquidated damages clause stating that there is a penalty if she breaks the lease, you can't even keep the security deposit. So, at some point, she will need to give you her forwarding address. Like I said, you have 15 days from the day she gives you that address to put it in the mail. If she doesn't give you the address....the money is all yours.
Some times it is easier to find another tenant than deal with a princess tenant....but, you should not have to lose money for that sacrifice.
Let us know what happens