Heidi Weinerman is Howard's older sister and the host of Norrisville High’s Heidi@School, where she updates everyone on what's happening at school. Her show includes a Gossip Report where Howard almost revealed Randy's secret identity as the ninja. She seems unable to remember Randy's name and calls him a name that sounds similar to him, such as "Andy" or "Sandy".
She is on the cutting edge of pretty much everything. She apparently likes attention and publicity since she spends most of her time on her show. She does not get along well with her younger brother, Howard, since she was annoyed when he came to ask her for lunch money in "Gossip Boy" and threatened to embarrass him if he and Randy would ruin the Norrisville High Talent Show in "So U Think U Can Stank". At first she believed that Howard knew the ninja's identity but got angry at him when he supposedly didn't.
Heidi is thought to be tall and beautiful. She has medium length orange hair and blue eyes. Her casual clothes include a beige blouse with a red collar and cuffs. She also wears a red skirt and white stockings with red shoes. She also wears a red hair clip on her right side.
She does not get along well with her younger brother, Howard, annoyed when he came to ask her for lunch money, and threatened to embarrass him if he and Randy would ruin the Norrisville High Talent Show. At first she believed that Howard knew the Ninja's identity, but got angry at him when he supposedly didn't, saying she knew he hadn't. She is rude and impolite to her brother and likes to challenge and insult him. Both of them enjoy popularity but she is far better at getting and keeping it. She doesn't seem to care about Randy when she's around him and Howard, showing how little she cares about her brother and anything involving him.
Although he says he's known Heidi his whole life, she seems to barely know him and always forgets his name, calling him "Andy", "Sandy", "Mandy", "Tandy" or "Rudy". She doesn't seem to care about him in the least whether he is with or without Howard. She is willing to make use of him, though if it's to her benefit. She uses him as a back up judge when Bash betrays her. Randy explains that his and Howard's escape isn't Heidi's fault, impressing Heidi so much that she thanks him--although, much to Randy's chargin, she still forgets his name. She also gives him credit, albeit messing his name up again, for apologizing to Theresa and giving her flowers in "Shloomp! There It Is!". However, she is disturbed when Randy--who at the time was NomiRandy--flirts with her.
When Randy is the Ninja, Heidi is very fond of him. She sings a song about him for the Battle of the Bands, and she usually has nothing bad to say about him, unlike his other identity.
While Heidi doesn't interact much with Theresa before "Shloomp! There It Is!", she is affected when NomiRandy ignores Theresa to flirt with her. When Theresa is stanked, Heidi becomes her target, much to Heidi's horror. She even tells Theresa that she barely knows "Andy," but it only angers Theresa because she said Randy's name wrong. Captured by Thersa, Heidi pleads to her to not hurt her because they're total biffers, although once the Ninja shows up, Heidi tells him to waste her. Since then, Heidi and Theresa can be seen chatting in the backgrounds of "Welcome Back Catfish" and "M-M-M-my Bologna", suggesting that they might be friends.
- In "McFists of Fury", it was revealed that she owns a secret piggy bank, which Howard used to buy his McTop.
- She can sing and play the guitar as seen in "30 Seconds to Math".
- She won the Battle of the Bands many times before.
- In the overview of the pool in "House of 1,000 Boogers" Heidi can be seen twice.
- Her show is sponsored by McFizzles in "Night of the Living McFizzles".
- She was the one responsible for the Norrisville High Talent Show in "So U Think U Can Stank".
- She is the host of the Word War I rap battle in "Hip Hopocalypse Now".
- In "McFear Factor", it's revealed that Heidi is afraid of looking like her mother when she grows up.
- Heidi is similar to Jazz Fenton from Danny Phantom and Candace Flynn from Phineas and Ferb because they are both bossy teenage girls, both redheads, and they are both older sisters to the main characters (on the other hand, Heidi is the sister of the protagonist's best friend, unlike Jazz and Candace).
- She is also similar to Lois Lane and Vicky Vale from the DC comics. They're both reporters and they have a lot of appreciation for their respective heroes.
- In McFear Factor Heidi's worst fear is looking like her mom when she is older - fat and slow.
- When Howard tells everyone to act natural as Bash comes over in "Pranks for Nothing", she does hand gestures. Later, the Prankzooka turns her cellphone into large speakers.
- According to a Tumblr post by RC9GN animatic editor Nico Colaleo, Howard is Jewish, meaning Heidi is also Jewish.
- Heidi is one of the only recurring students that never got stanked by the Sorcerer.
- "The only dish you know comes with sausage and extra cheese."
- "That was pretty juicy. I'll give you a splart."
- "You know who the Ninja is?!"
- "Howard! I knew you didn't know! Ugh..."
- "If you wonk this up, I will webcast that video of you two taking a bath together."
- "My guitar is missing! Has anyone seen it? It's light pink with dark pink skulls and a strap that says "Heidi Weinerman" in hot pink letters."
- "Howard! Now I'll never win!"
- "Zombies are hot this year. They're everywhere. Literally, everywhere."
- "But you look just like...my mom! (squeals in terror)"