Firstly how are her other skills? Things like riding a bike, skipping, -large motor skills and fastening buttons, sewing, manipulating small things- fine motor skills? She may have a problem called dyspraxia, if she seems very clumsy and has problems doing things. If this is the case you could ask the school to get her assessed.
You can still work on her writing, I suggest you start with looking at how she holds her pencil, you can buy special holders that fit on the pencil and help develop good habits. Then you could go right back to basics and begin by simply getting her to copy patterns, zig zags curves, vertical and horizontal lines. Also encourage her to paint and draw. Then move on to letter formation .
That said she may not improve a great deal. If her lack of ability is affecting the work she produces it might be worth asking the school about her using a computer for some of her work.