Delay to new tenant moving in

Tenancy Deposits

I have a tenant wanting to move in to a rental property. She has paid a holding deposit to my agent, who is providing a 'let only' service for me. Her current landlord is insisting that she gives 2 months' notice, as indicated on her current AST, but he has failed to amend the AST following a relationship break up. The AST is still in joint names. The deposit may or may not be held with a guarantee scheme, such as the DPS. My question is: Can her current landlord insist on 2 months' notice, should he have issued a new AST in my prospective tenant's sole name and should he have re-registered the deposit in her name only? What would the best advice be I can give her, as the delay is resulting in me paying the mortgage and bills, while being morally committed to renting the property to her, having accepted a holding deposit?