Like most opinions here I have to go 100% with power. A long time ago a company of mine had serious issues with a copier at a Government building. It would blow A/C power boards once a month regularly. After the 4th one went some bright spark decided to test the power supply. The live and neutral were reversed. However, the copier would put up with it and work OK until it just seemed to have had enough and then go bang. This looks sort of what you're getting with power. Just one more thought, does this woman live near a mobile phone transmitter, I mean REALLY near, as I've heard rumours of those seriously affecting some PC's.