There are a lot of different supplements that can help reduce the chance
24/7 pasture is ideal, obviously this isn't always possible so keep her out in pasture as much as you can (minimum of 5 hours though 10+ is recommended). If this isn't available try free choice hay. Get a large trough and make sure there is grass hay available 24/7. If this can't be done then feed hay in a hay net. Horses are grazing animals and need as much forage as they can get. These will help her out in the long run
You want long term maintenance plan. A constant supply of Lucern/alfalfa
A supplement such as u-guard would prevent it from happening again.