It's very difficult to be able to advise you without knowing what Sky have said the issue is. Normally Sky carry out a line test when customers report a fault, and if this had detected a fault it would have been reported to Openreach who are responsible for fixing it That can take a while depending on where the fault is.
And if there's a known fault affecting multiple customers in your mother's area, it would again be a matter of waiting for Openreach to fix it, I'm afraid.
It's unlikely that Sky would do nothing if your mother has called multiple times to report it.
