If she does get rid of the mould, she'll need to prevent it coming back.
Keeping windows open, even throughout winter, will help provide a good air circulation.
Does she dry clothes on the radiators?? Worse still, if she dries clothes in one room on an airer, with the door closed?? All that moisture coming off the clothes goes into the air and circulates around until it condensates on a cold surface. Steam coming from a boiling pan of water, having a shower, etc, all contribute to mould problems.
My advice - buy a dehumidifier. We have 2 (one upstairs and one downstairs) and they both get emptied roughly every other day. All that water that we empty out, would be circulating around our house and would eventually cause mould problems ......