I've used it for many years. It is great. I use it for my kids though. I feel that it is my right to know what they are up to online for their safety.
I don't know how I feel about using it with another adult. I guess I wouldn't mind if I had nothing to hide. But then there is the whole trust issue. Do you have reason to believe that she is "messing around" online?
She has had both an emtional and sexual relationship with different people at work as well as tell people she is emailing that she is single. but those are done from her laptop. I don't even know for sure if she uses our home computer fort anything but her banking, but I thought I would check.