Notes:

some fair points someone made.

Them: She shapeshifted her outfit in "Beach Party".

ME:True
though I assume that is far easier to do compared to extending her whole arm and increasing it's size.

Them:Why didn't Garnet do it then?

ME: That is a decent point.
The best I got is that she was making sure to keep her balance because everyone was latched on to her for support.
If she did try to grab jasper the weight shift could send them all sliding down into the hole.