I was a Teenage ALIEN

Oas is sent from her home planet of Zorca-twenty-three to save her brother Ralb from the worst humanoid known in the solar system--a teenage girl. With her traveling companions, Rotsen, a dandelion with an attitude who watches too many Sopranos reruns, and Lehcarr, a Venus Fly Trap with the nasty habit of eating her friends, they set off to locate Ralb.
Traveling through a black hole, Oas is transformed from her ananoid shape into that of a teenage girl. They land in Bedrocktown to find the teenagers aren't as bad as they feared--they're worse. Zen her handler has warned her to stay sway from pizza and popcorn, but she tries both, with disasterous results.
She needs to find her brother, figure out how humans kiss, save a town from an E.Coli outbreak, and meet Johnny Depp, not necessarily in that order. Then all she has to do is figure out how to get home, but are her ties to Earth too strong.