FYI, she's not supposed to be able to touch the ground while remaining in the saddle.

Top tube standover height determines if a bike is too tall for your legs, and with a women's mountain bike that likely has the sloped top tube, she should have no problem touching the ground.

The seat should be adjusted so that the leg is almost fully extended when the pedal's furthest away, like the 5-o'clock position. The knee should be darn near straight at full extension, but the hips should not sway while riding. If configured properly, no normal mountain or road bike will allow you to comfortably sit in the saddle while touching the ground. If a seat is too low, knee problems will ensue, and the inefficiency of each pedal stroke will make for a lot more effort (harder to push) than needs to be made.

If that's what she's looking for, check out a Giant/Revive, recumbent bikes, or some of the crank-forward comfort-cruisers. Those bikes have the kind of geometry where the seat can be adjusted properly while still remaining close enough to the ground to allow planting both feet.