I had an XD9 Service and XD40 Tactical. I disposed of them and now have an M&P9 and M&P40.
My wife had a hard time operating the slide on my XD9 Service size but does not have any trouble operating the M&P slides.
The M&P grip is adjustable XD's are not.
I had several thousand shots throught the XD's and have comparable through the M&P's
The XD's were good pistols but I prefer the M&P's by far.
If your wife is going to use it let her pick. You may have to purchase a second for yourself. Nothing wrong with that.