It could be alot of things. Several things that we've experienced at different times are:
1. When they built the house, there was nick in the cable (in the ground) that runs the power to the house. So, we had some of these odd situations with the fading lites and finally lost the power altogether. And, since this was in the old days and it was in the line outside the house, the electric company did fix it.
2. She should have someone out to at least check the A/C. A basic service charge will run her around $50, but she should start there. Those guys should even be able to check the basic power feeding the unit with the meters they have. We had an A/C unit that seemed to be running okay, but it also never seemed to really cool things down. There was a part that was malfunctioning, causing the compressor to sporadically get shut off, so the fan would keep running, but no cold air was coming out alot of the times.
3. During peak power time last Friday in Flower Mound, our power was cycling off every 5 minutes or so for about 30 seconds for a couple of hours. I don't know what was going on, but she could be experiencing something similar, although I would think she would notice if her power was going out totally and that experience did not impact the overall performance of our air conditioning. It did, however, keep shutting off my dryer.