Through The Waterfall: Book 1 Guardian Of The Realm

When Tess hunts for a toadstool from a fairy ring she never expects to meet the owners. When she notices out of place darts of brilliant color she races for home, not the least bit interested in meeting the residents of the Other realm. They follow her home and offer her the position of Guardian of the fairy demesne, which she promptly refuses.Somebody amongst the Others killed her parents and left Tess bound in a wheelchair for two years until Grandma uncovered her ability to Heal.
Trey, a fairy prince, arrives to present King Ral's offer to help her locate the creature that devastated her life and get revenge against it if she accepts the position of Guardian. She refuses him as well until Grandma, who raised her to be a witch, traveling the country to train with the best, encourages her to accept the offer. Tess gets sworn in and promptly finds herself off to slay harpies and fall in love with a prince.