Wrist problems can be caused by many things: improper form, change in technique, too heavy a frame, too light a frame, too high swingweight, too head heavy, too low swingweight, too stiff a frame, too stiff strings, too underpowered a frame (overswinging), and overuse (repetitive use) injury,. Her wrist problems may not be completely caused by tennis. Does she spend a lot of time using a keyboard or mouse?
With the Blade S, we can rule out stiff frame, too low weight and swingweight, and too underpowered. It very well may be too high a swing weight and too head heavy. Of course the two are related, but a higher swingweight frame without mass in the handle really can put extra strain on the wrist.
+1 on trying other strings first. By switching to a full bed of thinner gauge multi (17), you can help two possible causes at the same time by reducing string stiffness and swingweight (since multis are softer and lighter). Of course multis are typically strung a little tighter then polys to harness their power. There are some lower powered multis like Velocity that play a little more like polys if she wants more control.
String weight can really make a difference. I reduced the weight of my Blade 18x20 by 5 grams (10 swingweight points) just by going from a 16 to a 19 gauge poly, which is about the same weight as most 17 gauge multis. It's much easier to handle, especially on volleys. Since gut is heavier than poly I would avoid it.
If changing strings doesn't work, then try some lighter swingweight/more headlight frames that aren't too stiff or underpowered. In addition to the Clash, the Head 360 MP and Dunlop Revo CV 3.0 are a couple of frames that would be similar to her Blade S but easier to handle. The Dunlop plays much softer than its RA would suggest.
