Thanks, tomh. It's funny you should mention that because that's exactly what my mom thinks. We just talked about it before I went online. She remembered that we had a similar problem in that room many years ago except that time the water damage was in the ceiling next to the window. We had the section of roof above the window re-waterproofed. (What do you call that joint where two parts of the roof form an angle?) I guess it's time to do it again.
Gotta say I'm a little relieved that it's probably not the contractor's fault. It would have pissed me off royally!