Having worked with a person that did not have enough power in their fingers to turn the key to start a vehicle or unlock a door...
You could always screw on a bar as large as your wife needs to the front of the round knob on the frameless window openers. You could literally open and close the window with a closed fist.
With the sliding windows I think the finger action to unlock the window and grab the window to open it would take more finger power than might be available... if not now... maybe in the future.