What about a Crosman 2240?
You could put a trigger tune kit in and fit a 177 barrel and steel breach (or stump up for the 2300T and you'd get all that anyway). The important bit is that you could chuck the standard plastic grips and get some slim custom ones made for her. Not sure if the trigger pull would be too long though.
My 5 year old is getting into shooting and I've had to start her on rifles simply because with a bipod fitted she can shoot prone. Pistols are a problem, that Beeman is pretty light in the scheme of things!