She can eat the same feed as everyone else. The main thing is to not offer her extra goodies in between feedings and to make her work more. If your flock must be kept in a run, then place the water as far from the coop as possible, and if you can, do the same with the feed, but on the opposite corner. The idea is to make her move as much as possible. Ideally, she should free range as much as possible.
Your management of her is going to be lifelong. As long as she is a part of your flock, you will not be able to free feed. She can and will eat herself to death if given the opportunity.