Rick Nevill ...

^ I would like to to make a custom iambic keyer for a person with
^ quadraplegia. She mainly has use of only her index and ring
^ finger. She can only flex her thumb and cannot release the
^ thumb pressure at will.

My radio has a built-in keyer (Yaesu FT-897) so I made a simple key for it
out of two Popsicle sticks, some wood blocks, and a few nails. My key has
both a straight key and a paddle, one on each side of the block that holds
the Popsicle sticks. The tension is adjusted by moving the stick into or out
of the blocks that hold it. The nails provide tie-downs for the wires and
contacts for the keys.

It works well. Perhaps you can use something similar as a test platform to
find out what sort of key will work best for your friend.

Frank