Help with window replacement parts

Thumb button actuator and shoe as seen in images.

Not sure the brand, see no identifying numbers. Window guy told us should be easy to find on-line and replace ... so far as my 3 hour search says he is wrong lol!

This product you have 26-312 looks like it may work but according to my notes (as seen in images loaded) the measurements seem to be taken from a different place than what he measured or maybe I am wrong?

Just trying to help Grandma from have window trouble with least frustration and cost.

Please advise.

By the way - you have a terrific site - easy to navigate and very informative. Much appreciated!