I would just up her hay...Now depending on the size bales she is fed from, you may only need to add one more. Just experiment and see what seems to work best for her. Where I was at last year had the huge 120-150 lb square bales...my 15.3 hh QH cross mare ate 4 sections per day...1 am, 1 afternoon, 2 at night. She also got a 1 qt scoop of alfalfa pellets with her supplements in the am.
As far as upping the grain, that would not be "my" first choice...if you are giving it to give her the supplements, the amount she is getting is more than enough. Start with the forage.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."