Rhonda considers herself one of the most fashionable students at school besides Sid. However, she also falls into the same convention of several animated characters, namely, that she wears the same clothes (red shirt, black pants) all the time. Her parents Brooke and Buckley (Lori Alan and Sam McMurray, respectively) are wealthy, and she frequently holds parties at her house ("Helga's Makeover", "Hey Harold!", "Cool Party", "Helga's Masquerade").
However, Rhonda does have her flaws: she has been known to be "pushy, self-obsessed and materialistic" ("Polishing Rhonda"), and she has strong discrimination against so-called geeks, such that she forces them to the back of the bus like how African-Americans were back in the 60s ("Rhonda's Glasses") and maintains a list of cool kids and geeks ("Cool Party"): she and Arnold are the only major characters on the former list, and Gerald (ostensibly, among the cooler kids on the show) is on the latter list (she's had a personal grudge against him ever since he ran against her for class president).
Whereas Arnold and Helga's best friends (Gerald and Phoebe, respectively) also have major character status, Rhonda's best friend Nadine (Lauren Robinson) is a relatively underused character: she only had speaking roles in 7 stories, one each in the show's final two seasons ("Dinner for Four" in season 4 and "Rhonda Goes Broke" in season 5), and no focus roles. Nadine's most distinct feature is her spider-shaped braids, which is somewhat fitting, since Nadine is the fourth-grade nature expert, with a special interest in insects (she has a pet tarantula as well as a collection of cockroaches and can sometimes be seen with a butterfly net).
Despite her wealthy upbringing and tendency to belittle others, she has been known to play contact football and a variety of other sports along with the other children - until she was enrolled in an extracurricular session to improve her manners, she was also quite rude to others, whether intentionally or unintentionally.
There's also implied that Rhonda would be related romantically with Harold. In the "Operation Ruthless" episode, we can see Rhonda pulling Harold to the Love Tunnel's boat while saying "I know you like me, Harold", while Harold tried to resist. Several episodes later in "Egg Story", Rhonda and Harold are assigned as work coupe to take care of an egg. Then Harold reminds her about their moment in "Operation Ruthless", and Rhonda trying to keep him shut up. The egg experience ended with Harold frying the egg and tried to rejoin the shell. Rhonda first got mad and then forgave Harold and both shared a special look to each other. In addition, Rhonda occasionally makes critical remarks toward Harold, both in and out of his presence. This could hint at an attempt to conceal her feelings for him, much as Helga does with Arnold.
Rhonda's glasses Edit
Among the most blatant gaps in Hey Arnold!'s continuity concerns Rhonda getting glasses (rather blocky ones, at that) after getting a bad result on her optical examination, rendering her a geek, the very type of person she has always discriminated against ("Rhonda's Glasses"). She had never shown any signs of optical problems before this episode, however. Also, by the end of the story in question, she has a more fashionable pair. However, from her next appearance onwards (in production order "New Teacher", in US airing order "What's Opera, Arnold?"), she appears as she had appeared before that story (i.e., without glasses, blocky or otherwise).  "Cool Party" seemed to be the most appropriate story to feature her glasses again, since it also deals with her constant discrimination against geeks, however, they're nowhere to be seen, especially when she's actually at Arnold's party for geeks herself (where her "blocky" glasses would have seemed perfectly welcome).
In "Rhonda Goes Broke," she says she was looking for her contact lens in the garbage, hinting that she may have gotten contacts. It should be noted, however, that she had been using this as an excuse for looking for cans to recycle, at the suggestion of her father.