This dog is only seen once, in a brief scene in WishologyThe Exciting Middle Part, when Timmy waves hello to her while she passes by his house. She is seen with her dog, a light purple colored French Poodle, near a fire hydrant. Trixie yells "Help! Security!" and then runs off pulling her dog along with her. The dog has not appeared since.
Trixie's dog has puffy whitish purple fur and a long nose and tail.