In "Cartman's Mom is a Dirty Slut," it is implied at the end of the episode that she had sexual intercourse with Liane Cartman, which made her a potential mother of Cartman, but as a result of "201," it is revealed that Liane was Eric's mother.
Crabtree was, for the most part, a background character, used only for the occasional joke or for scenes on the school bus. However, she received a prominent role in "City on the Edge of Forever (Flashbacks)", when upon driving the kids back from school, she takes the bus off the main road and ends up getting it stuck on the edge of a cliff. Crabtree immediately goes to get help for the kids and orders them to stay on the bus in her absence, by threatening to kill a bunny. While the students have assorted flashbacks relating to past adventures, she makes it to the main road and is picked up by a trucker, whose truck is delivering Roofies. She takes several, believing them to be aspirin. However, the drugs only seem to calm her slightly from her normal insanity. She begins a relationship with the trucker, thus forgetting about the kids, and begins life as a stand-up comedian on The Tonight Show with Jay Leno. However, she finds the life empty and goes off with the trucker to watch the sunset. At the end the episode everything, even Crabtree's own story is implied to be a dream of one of the boys, which she and the trucker acknowledge sadly.
In the episode "Fat Camp," Kenny was supposed to crawl into her uterus and stay there for six straight hours before coming out. She was excited about being on TV, adding that she hadn't had this much attention paid to her cooch since she was 16. Later, when Kenny's lookalike, came out of her uterus dead, she said: "I told you I was a tight virgin flower." This is a continuity error - not only are the quotes contradictory, but Ms. Crabtree had sex with Chef in "Chef Aid," although he has her wear a bag over her head (most likely to avoid having sex with her).
Her final surviving appearance was in "The Simpsons Already Did It," driving the bus and surprising Butters in a Simpson-ified form of herself. She only screams a few times, then drives off.
Ms. Crabtree was murdered, as well as the bird nesting on her head, with the left hand and wing missing, by Michael Deets in "Cartman's Incredible Gift." Officer Mitch Murphy commented "She was considered an ancillary character. One the fans wouldn't miss much." Harrison Yates also yelled, "She may not have been in any recent episodes, but dammit she deserved better than this!", poking fun at her lack of recent appearances at the time. This also marked one of South Park's few moments of breaking the fourth wall. The school bus driver position was then evidently taken over by Jose Venezuela, as shown in "Ginger Kids."
She wore a blue sweater and green trousers. She had crooked yellow teeth, baggy eyes, an angry expression (most of the time), and messy, scraggly dark brown hair, which had a bird living on it. (In "Fat Camp", it is revealed that she has brown socks). She also appeared to be slightly obese.
Ms. Crabtree appeared to be mentally unstable. She is usually cranky and she constantly screams at the children on her bus and always angrily asked, "What did you say?!" after they insulted her. Occasionally, she screamed blindly at the students to intimidate them. In later episodes, she appeared to be slightly calmer and rational. It may be possible that the reason why she is strict and she yells so much all the time from watching training videos as shown in "City on the Edge of Forever (Flashbacks)".
- "Sit down and shut up!"
- "What did you say?!"
- "Y'all be quiet or the cute little bunny dies!" from "City on the Edge of Forever (Flashbacks)"
- "You look like a lump of dog shit just got hit by a CAR!" from "City on the Edge of Forever (Flashbacks)"
- "I haven't had this much attention paid to my cooch since I was 16!" from "Fat Camp"
- Executive: "How would you like to make a million dollars, baby?"
Ms. Crabtree: "How'd you like to suck my ass!?" from "City on the Edge of Forever (Flashbacks)"
- "Be quiet back there! These roads are slick!"
- "GOD! Oh, for Christ's sake, I don't believe this!"
- The character may have been inspired by the school bus driver in the 1994 film Forrest Gump, who was abusive and also had a bird in her hair.
- In the original promo for "The Succubus", Ms. Crabtree was shown to be the new chef instead of Mr. Derp.
- In South Park: Bigger, Longer & Uncut, her pants are black rather than the usual green.
- The only episodes where Ms. Crabtree is shown to be happy are "City on the Edge of Forever (Flashbacks)", "Mr. Hankey's Christmas Classics", and "Fat Camp."
- Ms. Crabtree had a speaking role in 12 episodes by the time she was killed off.
- In Season One, Ms. Crabtree's pants are rather tan instead of the current green.
- In "Fat Camp", it is shown that she has brown socks.
- In early seasons, Ms. Crabtree's eyebrows used to be black but in later seasons, they're brown.
- In "Chef Aid", her house is shown to be yellow.
- Her last name is meaningful. She is very crabby and a bird nests in her hair as if she were a tree.
- Despite her angry nature, she is shown to care deeply about the kids as seen in "City on the Edge of Forever (Flashbacks)".
- Ms. Crabtree was the first character to be voiced by Mary Kay Bergman.
- She is the first female character to appear on South Park.
- Ms. Crabtree shares the name with the teacher from "The Little Rascals", who also has the same name as her.
- According to "Fat Camp", it is implied that she had underage sex when she was a teenager.
- "The Unaired Pilot" (voiced by Karri Turner)
- "Cartman Gets an Anal Probe" - Drives The Boys to school.
- "Weight Gain 4000" (cameo) - Seen driving the bus.
- "An Elephant Makes Love to a Pig" - Tells Kyle's elephant that he can't get on the bus and will have to ride on the special needs bus.
- "Cartman's Mom is a Dirty Slut" - Stan Marsh, Kyle Broflovski and Kenny McCormick tell her that their not getting on.
- "Cartman's Mom is Still a Dirty Slut" (cameo) - Stated to be one of the mothers of Eric Cartman.
- "Ike's Wee Wee" (cameo) - Drives away screaming.
- "Conjoined Fetus Lady"
- "Chef Aid" - Chef has sex with her for money.
- "City on the Edge of Forever (Flashbacks)"
- "Roger Ebert Should Lay off the Fatty Foods" - Drives the class to the Tantalus V. Observatory.
- "Spookyfish" (cameo) - Seen driving the bus.
- "Rainforest Shmainforest" (cameo) - Seen driving the bus.
- South Park: Bigger, Longer & Uncut (cameo)
- "Mr. Hankey's Christmas Classics" (cameo) - Seen during the final song.
- "World Wide Recorder Concert" - Drives the third grade class, Mr Garrison and Mr Mackey.
- "Trapper Keeper" - Seen driving the bus to school.
- "Fat Camp" - Impostor Kenny climbs up her uterus and stays there for six hours.
- "Towelie" (cameo) - Seen driving the bus.
- "Osama bin Laden Has Farty Pants" (cameo) - Seen driving the bus.
- "Fun with Veal" (cameo) - Seen on the bus at the beginning of the episode.
- "The Simpsons Already Did It" (final speaking role) - Seen driving the bus.
- "I'm a Little Bit Country" (cameo) - Seen in the crowd, near the end of the episode.
- "Goobacks" (cameo/obscured)
- "Cartman's Incredible Gift" - Murdered by the hands of Michael Deets, making this her final appearance.