Nearly 10 years ago, I watched a movie or short telefilm on TV. I have forgotten most of it, but I am providing highest detail possible based on my faint memory.
The story was based on a novel (as displayed in the intro or outro.... name not in my mind). It was floating around a cute blonde girl having age below 20 (my guess). She was new in town (filmed as small US town). She was a beautiful, kind, nice girl with a soft British accent. So, everyone liked her (including me outside TV).
She got some kid friends who started to be curious about her because very little was known about her... no family... nobody entering/exiting her home. One day, they invaded her home and got caught by a gorilla that just came with a bike. He was actually her family member (perhaps brother) in a gorilla suit. Kids got afraid at that time but increased their rate of invasion.
Time passed and society started to believe that she was alien (not seriously). I've forgotten what led to this conclusion. Anyway, she sensed it and started to socialize with society. Until the last scene, everyone thought that she was a normal human.
But, one day... she left everyone and was gone. I still remember that last scene: She was standing on a beach under a big saucer. She was weeping while surrounded by people. And, the saucer beamed her up and she was gone. She was really an alien!
The movie/telefilm title was something similar to this: {Name of girl} Was an Alien.