I would just take your time with it…it sounds like you are aware, doing the right things to help. My lefty son had a terrible grip. (I am a righty…yes, cursive was FUN to teach!! 
) Anyway, we used the triangle grips and the soft rubbery grips in Kindergarten to get him to change his hold. It’s fun to get crazy colors to add to the interest. Now a teenager, his grip is still different than mine, way improved over his 5 year old grip, but it is his grip, his printing is very neat, and he does not complain about hand pain at all. The key for me was to release “MY GRIP” a bit and encourage more…if you know what I mean.
