In ToonWorld, she is 11 years old, but in PB&J Otter and its revival The New Adventures of PB&J Otter, she is depicted as being 5 years old.
Jelly's current 11-year old self is voiced by Ashleigh Ball (who also voiced both Applejack and Rainbow Dash from MLP: FiM), while her younger 5-year old self is voiced by Ava Acres, although she was originally voiced by Jenell Brook Slack in the 1998 "PB&J Otter" cartoon.
Jelly is a slender magenta otter with a white muzzle and belly, a black nose, and indigo hair. As a 5-year old, Jelly is strangely taller than her brother, Peanut, who is older than her. Jelly doesn't usually wear a lot of clothing, other than black and white shoes with pink socks.
As an 11-year old, Jelly now wears a yellow T-shirt with purple sleeves and pink trim, blue shorts, and black bands around her ankles, since she now prefers to go barefoot. Her hair is now very long and scruffy, and almost reaches her shoulders.
In her ToonWorld debut, Jelly was shown to have been aggressive and crazy, since she was somehow kidnapped and brainwashed by Madame Mousey. At the time, Jelly had shaggier fur and hair, and her left eye was scratched out in a fight, which left a scar on her left eye. In ToonWorld All-Stars: The Movie, Jelly was often shown alongside Madame Mousey, implying that the former may have been a minion of the latter.
However, in ToonWorld All-Stars 2 (which is still in development), Jelly gets tired of Madame Mousey treating her like a slave, and betrays the E.V.I.L Troop. After reuniting with Peanut and Butter, Jelly soon redeems herself and becomes a good guy, err, gal.
Prior to the ToonWorld All-Stars movies (and also after she redeems herself in ToonWorld All-Stars 2), Jelly is shown to be caring and is the brain of the family, who often solves ideas and helps out. She is usually the one that suggests doing a "Noodle Dance" and is often the one to come up with ideas. In "PB&J Otter", Jelly usually plays with Pinch Raccoon, but because of Jelly's tomboy attitude, she isn't always in favor of some of Pinch's more "girly" pastimes, such as giving makeovers.