If they come (which is unlikely - these letters are often part of the technique to frighten people) she must not let them into the house. She tells them that you are the debtor and don't live there any longer, and that none of your possessions are there. She will be asked for your present address. She either says she doesn't know, or she gives it to them or she says she is not prepared to tell them. They cannot make her give them any information. If they try to harass her she should tell them to leave and say that if they don't she will call the police.
As Ethel says, it would be far better if you gave the creditors your address and started dealing with the problem yourself.
Debt Collectors have no powers at all, they are not bailiffs, your Mum doesnt even have to speak to them, she can tell them to go away and if they dont she can call the Police to remove them.
Have you thought of contacting Payplan to help you with your debts? They are very good
Big John, same thing happened to me. I had 40k worth of debt at my parents address. In the 3 years since that happened, no bayliffs have called, any post that is addressed to me gets returned saying no longer at this address living abroad. They will soon get fed up with chasing. I'm not on the electoral register, am untraceable through tax and Ni because of data protection, the only drawback being I can't get credit but I don't need any.