At similar 'specs' to your lady, I started on a 9'5 Nash mana and progressed from there. Used it initially for flat water paddling but when I started to catch waves found the size way too much for me and couldn't do much on the surf except for get on a wave. I now ride the starboard converse which I totally love! It's really stable and long enough to paddle on flat water. I have the 9'0 but they are doing it in the 9' 5 now also. Being the same size as your girlfriend I would go a little smaller than 10' especially if she is considering catching waves.