Welcome to Barnmice Cindy!

You can ask for advice on our Forum.  Have you had your mare's teeth checked?  Had her on a regular worming schedule?  (You will be asked this on the Forum so give some background on what you have done.)

Whenever I wanted to put weight on a horse I would add corn to their feed, not much, 1/2 pound to a pound every feed.  The horses really LOVED chomping on their corn!

Be sure not to get her too fat (yeah, I know, this is a long way off.)  Too much weight can put strains on their legs.  If I could not feel the horse's ribs through their fat I put them on a diet until I could see traces of their 1st three ribs behind the elbows.