I'm with JDI, just cut back on her feed. Get a scale and measure the weight of the grain you are giving her. Cut it a bit each week, keeping an eye on her weight. If she isn't dropping any cut it more. If she starts to lose too much, bump it up a bit. Its OK to use a scoop but do a weigh in on how much goes in the scoop. Mark a pound, 2 pounds etc, on the side of the scoop.
My kids started getting chubby when they came in off the pasture this fall and started on hay 24/7. I was only feeding 1 pound and have cut it back to half to maintain them. I'm guessing you could do the same.
Do not cut back on the hay.
"Until one has loved an animal, part of one's soul remains unawakened..."
- Anatole France