"bumping" this for you with a few ideas.
Would he be willing to play with her----on her level down on the floor? How about walks with just him? Little treats? Time alone when you go do some shopping? Not an expert, though.

I have a 3 lb. senior girl who hates my dh unless he is on the floor at her level. Then she goes over to him for belly scratches. (Got her at 9 mo. from a puppy mill.

) Joanne
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Joanne

Eli

Chipper

Eva

Snowboy

Rosie(R.I.P. 1996-July 29, 2013)

Cocoa(R.I.P 1998-April 26, 2012):