To me her weight looks perfectly fine, if a bit pudgy- but she needs quite a bit of muscle- which is why she has that 'saggy' light look to her. Once you develope a good topline and some hindquarter/shoulder muscle, I think she'll look a ton better. She's quite cute though, with very unique coloring!
Is she ridable? If so, a 10-15 minutes walk every day, graduating to trotting and doing hill work would do her a lot of good.
Thanks, and yes, she's very rideable! We've done some trail riding with some hills - a couple of hours is our longest ride. I try to do that once or twice a week. Most days, it's fairly light arena work. I just got her up to some loping, it took a while because she's very green and is just now slowing down at the lope instead of trying to run full speed. She still bucks a little when we start a lope which is cute because it's not a "real" buck, just a head shake and a little kick up with her heels. She's beginning to collect herself nicely after that little outburst though.