"How many times have I have to tell you, missy, the TRUTH can never be known!"
She is first seen in Operation: R.O.B.B.E.R.S., where it's implied Numbuh 4 had a crush on her, and she is seen being disgusted by Numbuh 4's spelling homework (but since the Delightful Children had everyone's homework stolen, she believed the Delightful Children did the lousy spelling and berated them, instead).
She was given a cursed green necklace by her angry ex-husband. After she put on the necklace, she became possessed by the Queen of the Weredogs, and her house turned into a giant doghouse mansion. Following this, Mrs. Thompson had turned several other students into weredogs, most of which are on the Honor Roll. She was first seen in Operation: R.O.B.B.E.R.S., but her status as a weredog was not seen until Operation: H.O.U.N.D., and the origin mentioned above revealed in Operation: D.O.G.H.O.U.S.E.. Numbuh 4 is known to have a crush on her.
After the incident with fellow weredog Valerie, Mrs. Thompson had Numbuh 5 turned into a weredog while she was looking for the Cinder Block the KND use for their "Cinder Ball" games. Mrs. Thompson struck a deal with Numbuh 5 for her to steal all her teammate's homework and give it to her and her army of weredogs in exchange for being returned to normal. When the KND discovered this and confronted Mrs. Thompson, the necklace was taken off of her and the Curse of the Weredog is broken and all those affected are returned to normal.
- In Operation: D.O.G.H.O.U.S.E., Mrs. Thompson repeatedly says, "I probably shouldn't have told you that/said that." as a running gag due to the fact she can't help but give an honest answer to any question given to her.
- Mrs. Thompson's running gag in Operation: D.O.G.H.O.U.S.E. is possibly a reference to Hagrid from the Harry Potter series (namely the movies) as Hagrid would often give classified information on accident to Harry and his friends, then instantly regret it, leading into Hagrid's famous lines "I shouldn't have told you that" and "I should not have said that."
- Her necklace was actually a gift from Ex, most likely given to her after they broke or divorced as a parting "gift"