The benefit for her is the same as the benefit for me. I would like to keep as much of my life as private as possible. I am not sure bare Windows is the best way to achieve that goal ( even if she does not think it is relevant, her disregard for privacy considerations kinda forces me to put some blocks in place ). In case you are wondering, we have discussed privacy implications, but I am learning to pick my hills carefully.
Out of the two evils, I would sooner do Windows ( because then at least I can gut it ). I wouldn't be able to do it Chromebook. Separately, she already said no to Macbook ( so at least she is consistent - no OS change ).