I would think that a string instrument would be FAR harder physically than either a keyboard or woodwind instrument.
It all depends on the individual manifestation of the hand strength, I think.
DD really struggled physically with violin when she was 7. I now think that this may have been because of a lack of stability in her hands and wrists. While we never noticed any particular difficulty with piano that way, what we have noticed (and only started to note about four years into things) is that she has sharply limited pain-free practice time. That will eventually be limiting, and it's why I'd recommend choosing something which minimizes the conflict between instrument demands and disability. A physical disability isn't going to go away after so many years of instrument instruction, KWIM? And at that point it becomes a barrier and a source of deep frustration because of the limits that it imposes.
(We're there, with piano, in fact.)
