This is what tripods and remote releases are made for, steadying yo’ shit.

Also, I just checked, and it’s quite easy for me to hold Nikon DSLRs (D300 & D810) up to my eye, using a vertical grip / extra battery pack, in the horizontal position using my left hand only, and trigger the exposure with my middle finger. However my hand is probably larger so it might be more awkward for her. Either way I wouldn’t recommend it in the field without a strap around my neck.