I think a dental usually runs around $60-100. On a 3 year-old it really isn't necessary, but wouldn't hurt. At the young age of 3, dogs are usually pretty healthy to go under anesthesia. If you routinely made it a habit to get a dental once every few years, or just used something to keep her teeth clean inbetween checkups, then it would reduce the pains of her having to go through it when she's older.