I'm not trying to be mean or snotty, but as the owner, it is your job to know what condition your horse is in. Learn how to do a Body Condition Score, and do it every week. Here's a video if you don't know much about it. What's Your Horse's Body Condition Score? | Video | TheHorse.com
As far as what else she might need, that really depends on what she's getting from her pasture/hay. The best way to go is to have it tested. If you are in the US, your local extension agent should be able to help you with that. Many places are deficient in certain nutrients, but it's really hard to gauge what to add if you don't already know what's missing.