My wife is 5'3" and recently shopped new bikes for XC/Trail riding. She decided to go FS, because she still rides the hardtail she won her division in the Cactus Cup on. Like she should, she sizes her bikes off the effective top tube length, the standover, the total cockpit and the angles (important for short folk that don't want too much toe overlap). Since I went along, here's what I think your wife should look at:
The XS "Genesister" Fisher Cake (also called the 13").
The Women's geometry Specialized FSR
Santa Cruz Juliana SL (superlight) in medium
Santa Cruz Superlight in small
Santa Cruz Blur in small
Titus Racer X 100 in small
My wife went with the small Blur, which didn't have the standover she wanted, but just enough. She likes the ride and the way it climbed in her tests, and has been riding it since December, using her TALAS at 100mm and with the 5th Element Air.
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