A 'standard' arrow, to maintain original spine, is 28" from valley of nock to base of head, with a 125 gn head. Shorter than that with a lighter head increases spine (stiffer) and longer than that with a heavier head decreases spine (less stiff).
What is her draw length? Make the arrow 1" longer than the shooters draw length, and then fine tune arrow flight by changing point weight. Arrows impacting left are too stiff, arrows impacting right are too soft.