1997 Volvo 850 speedometer-turn signals-electric windows

My wife has complained that her 97 Volvo 850 sometimes has problems with the speedometer, turn signals and electric windows not working all at the same time. I have driven the car many times and have never experienced this problem. It seems to happen with her and then it starts working again on its own. I just recently replaced the alternator so I sure it has nothing to do with that because it has happened before and after the replacement.

Thanks
Bill Waulk