If you google plantar warts you will find a huge variety of treatments. The most popular one seems to be putting duct tape on the wart, cutting off it's oxygen supply. Then scrapping it off, applying more duct tape, repeat until gone.
You can purchase stuff at the store to apply to it to help kill it (like Dr. Scholl's Clear Away Plantar, Salicylic Acid Wart Remover for Feet).
I have a plantar wart and knew nothing about them. When I showed it to my PCP at my annual she recommended I see a podiatrist (which I currently am). The podiatrist put some heavy duty salicylic acid on it and told me to leave it wrapped for 48 hours. She prescribed a drying solution that I apply nightly. I went back today (2 weeks after my first appointment) and she scrapped off a huge chunk. In 2 weeks I go back and she will scrape the rest of it out of my foot.
As my plantar wart is slowly dying it is turning a dark brown color and gotten smaller. Previously I was growing callouses over top of the wart, making it raised.
The whole experience has taught me to never, ever go without shoes.
Good luck to your DD.