She can do what she likes I suppose, but your best bet is to have a formal re-direction of mail, with Royal Mail.
They will still deliver mail addressed to the house, and/or mailed addressed to Mr/Mrs, or just Mrs. But anything with your name only on it, should be diverted as per your instructions. Make sure that you make your instructions clear....visit to local Sorting Office and speak to the Manager.
My other advice to immediately get in touch with everybody that might send you a letter, Bank, Building Society, Insurance company, etc, etc. Register a change of address with them directly as well as Royal Mail....belt and braces and all that.