1) Since she was your tenant at the prior place (you were her landlord) *and* you allowed her to move out early (you in fact asked her to move with you), you do owe that that earlier deposit back: when a tenancy ends (e.g. that that subtenancy of hers ended), if the tenant (or subtenant) did not owe the landord unpaid rent or for damage to the property, the tenant gets her security deposit back.2) If she owes you rent (hasn't paid for any months she lived here) for the current location, you could do any/all of a) evict her for unpaid rent; b) take any unpaid rent out of her *current* security deposit, if there is one; and/or c) sue her for the unpaid rent.Each tenancy is separate and must be evaluated, dealt with, etc. separately. They were for totally different units or homes; the fact that she was renting (or subrenting) both from you does not roll them together into a single tenancy.If she sues you for the first deposit back, she will very likely win and you will have to pay her that money, and likely some extra (generally, tenants get extra compensation when a security deposit is improperly withheld); you could countersue for any amounts (e.g. unpaid rent) she owes you; and what you owe her and what she owes you will be netted out against each other.