Lily Lightly has something known as a Magical Imbalance. Its when the magic within a pony is unstable enough that it will appear in other ways- Whether that be blasts from a Unicorn Horn or an unusual amount of speed or strength in Pegasi or Earth Ponies. Luckily, there's things to assist. What Lily Lightly has is an enchanted device that makes the Unicorn Horn unable to use magic. Therefore the remaining unbalanced magic instead appears through her mane and tail.
She is shy because of this, often preferring to be alone and out of sight from the general public due to her out-of-the-ordinary instabilities. Despite her situation though she does quite enjoy gardening, so more often than not you can find her in her back yard tending to the many plants she has.