What about trying writing with different mediums for variety? So markers (dry erase or not), chalk (sidewalk chalk or smaller), crayons (triangular, jumbo, small, etc), paintbrushes, pens, and so on. All can be done large. Drawing in rice/beans/sand with fingers or craft sticks. I don’t know if any of it wll help, but variety is always nice. Also working on finger strength with various model magic/playdoh/clays (some are super soft and easy to manipulate while others take more strength), beading large wooden beads on pipe cleaners, plunking around on a piano (pushing against the weighted keys). My kids also like thinking putty – they have color changing ones that would change as she warms them up with her hands in use, there is magnetic thinking putty, and more.