I think trying a BP&W is a good way to go. If she doesn't like it, I would echo the others on this thread that said a women's BCD made a lot of difference for them.
I originally had a men's jacket BCD, which did not fit well at all. The problem was the length - it was long enough that the bottom started to overlap my hips, and the cummerbund hit me extremely low on the waist, where my hips were starting as well. When I tightened it as much as I could because of my hips, it was not really tight enough on my waist. As soon as I got in water and things could move a little, it would end up floating up on me, flopping around my waist area, and feeling like it was restricting my arms and head. I just couldn't keep it in the right spot because of my body's shape where it needed to sit.
I got a Tusa Selene, made for women, and it made a tremendous difference. It was cut short enough so that I could tighten it properly around my waist, and then it didn't budge in the water. I am 5'8" and relatively long in the torso, so I would imagine that if I had this issue, many other women would as well. My current BCD also would be more forgiving in the chest area if space was needed, although I didn't have a problem there.