Since you have proud flesh just starting, I wouldn't go with any of the caustic powders like wonder dust. Talk to your vet and get a combination antibiotic/steroid cream. Where caustic powders will damage healthy horses along with proud flesh thus slowing healing, using a steroid will simply prevent proud flesh from forming in the first place and doesn't slow healing.
Also, you need to look at what is causing the proud flesh. If this wound is near a joint then you need to stall her while it heals.
Licensed Veterinary Technician