Thanks for all the feedback everyone!
She is actually already starting to tone up and is looking nice, and I decided to do what everyone's said -- not worry so much about her weight so long as her health is fine and the extra lbs aren't causing any issues. I have been giving her sugar-free peppermints (in moderation), and every once in awhile someone at the barn will offer her a piece of an apple which I don't think is going to set her back too much!
It does get cold here in winter (it's been in the 20's and 30's lately and winter hasn't even really started yet!), and we have about a foot of snow on the ground already - so I think I may take the "wait until summer to shed lbs" advice and keep her warm & happy!
Hey has anyone put one of those Jolly Ball treats in their horse's stall before? How bad are those for them...are they basically pure sugar? I'm thinking she can't really have one, but I'm looking for other ideas about what I can put in her stall to avoid boredom. There's a Jolly Ball on a string in there now but I don't think she touches it...but she DOES love her peppermint-flavored mineral block!!