Legal Question in Landlord & Tenant Law in California

Small claims judges have a range of discretion in how they apply law and common sense, so it somewhat depends upon the judge you get. If you can show the judge that the plan was that she would stay the full term of the lease, such as an email where she (not you) stated that she would stay, you might win. Was there an exchange before she moved in that shows she knew the lease term and agree to share the full term? Did she admit in writing that the deposit should cover the remaining two months? Another point is whether she gave you proper notice before she moved out--generally, a full rental payment period (if she paid by the month, one month) is required. If she did give proper notice, then she might be able to claim her full deposit back, less a deduction for the bills you can prove.

Be aware that if you sue her in small claims and she countersues for the deposit, it is possible that the judge would require you to give her money. That's one of the risks of this type of litigation.