If her hands are small she may struggle to grip them (my sons did). Thumbies can be twisted with the whole hand and may be worth considering. I swapped the Gripshift on the 20" Islabike to an old 6 speed thumbie and we had no more problems.
My son had no problem on his Beinn-20L (7sp) and his now Beinn-24 (8sp but same shifter) both used the newer 3.0 Comp.
SRT600 vs SACHS Wavey.
I have and use both*, I prefer the SRT600 myself.
The Waveys are a bit chunkier and have a simpler cable change, some (or one) has a spring assist to help with the shifting. They are nice for a leisurely riding bike if you use a glove setup that finds shifting SRT600 hard in the wet for whatever reason as you can move to the large diameter section to get a better grip to change.
I intend to use a SRT800/600 hybrid on my next setup
*actually I use neither at the moment as they were both stolen (altitude and alu-o in my sig if you want to see the setup)