Legal Question in Landlord & Tenant Law in California

She is not allowed to walk away from her lease, but you must mitigate your losses. What this means is that she is liable for rent until you can find a replacement tenant. You are obligated to take all commercially reasonable steps to find a new renter as soon as possible. As long as you do that, she must pay you rent until that tenant starts paying rent, plus your documented out-of-pocket costs of finding the new tenant. There are special rules for service people who are being reassigned, but none of that would apply to a person she who is not in the military themselves or their spouse.