She is a Virginia Opossum (Didelphis Virginia), a Marsupial and has blue eyes.
Heather is embarrassed by her father for playing dead in response to even the slightest things that happen to him (such as a sleet of snow falling on his head). However, she seems to become less embarrassed by him by later in the movie, or at the very least, grow closer to him and understand that their species' tendency to play dead can actually be useful as opposed to something to be ashamed of, since she uses it to trick Gladys while they're infiltrating their home. She may like RJ.
Initially, she and the other animals are scared when they discover that during their hibernation, there has been major development in their neighborhood, greatly reducing the amount of forestry, and they fear they will be unable to forage for food in the small glade. RJ shows them the amount of food humans consume and waste and suggests they forage from the humans. Verne is hesitant but the other animals acquiesce. They make bold attempts to steal food directly from the humans, with RJ secretly guiding them to help collect the food he needs to replace Vincent's stash.
When the animals raid the trash cans of the homeowners-association chairwoman Gladys Sharp, she calls an animal exterminator named Dwayne LaFontant, who offers to install an illegal, lethal trap called the "Depelter Turbo" in her backyard. Verne sees this and tries to warn the others, but RJ insists they will be okay.
After a brief argument, RJ and Verne make up and RJ rallies the others to raid Gladys' home on the night before a large party. With Stella disguised as a cat to distract Gladys' own cat, Tiger, the others enter Gladys' home and collect all the food. While RJ inadvertently reveals his duplicity to the animals, Heather ends up using the playing dead technique to trick Gladys, which causes her to run to the bathroom and throw up. She does it convincingly enough to even make Ozzie think she's dead, but when he checks on her, he discovers to his great relief that she's okay and finally putting what he taught her to use. However, they are subsequently captured by Dwayne along with the rest of the group when Gladys calls him up, while RJ escapes with the food that he needs to collect for Vincent.
However, RJ has a change of heart and goes back to help them, which results in him and the other animals breaking free, and Spike, Bucky and Quillo use skills they learned from a video game to drive the truck back to the development. RJ pleads to be let in the truck as Vincent tries to catch him, but the others, angry at his treachery, refuse. Verne convinces the group to forgive RJ since he came back to save them. They return the truck to the development, crashing through Gladys' home, and the animals flee into the hedge. Gladys and Dwayne converge on the animals from one side with a String trimmer and a Cattle prod respectively, while Vincent tries to swipe at them from the other. Ultimately, thanks to some quick thinking from RJ and Verne, and Hammy assisting them by aligning a variety of objects while moving at the speed of light, which he's able to do after finally being allowed to have an energy drink, all of them get caught in one of their own traps and are subsequently stung by the Depelter Turbo. Afterwards, Vincent is taken to the Rockys, while Gladys and the Verminator are arrested for using illegal traps. The rest of the animals then formally welcome RJ to stay with them as part of the family.
It's unknown if Heather has a mother but, most likely she lives with her dad.