Why is my friend acting this way?

I have a friend who acts very strangely. She's 11 and acts like a five-year-old. She does really well in school and she's really smart. But when it's not school, she talks about weird stuff. She thinks fire-breathing squirrels are gonna take over the world and eat her pillow. She "didn't know" cows ate grass. She didn't know penguins have tails. She talks about waffles. A lot. My only guess is that she really needs attention. But why? What does it matter? There are more reasons, but these are the main things. I'm really concerned about her cuz I'm scared that she might have a mental disorder or something. Um... I just need some opinions here if you think she should visit a psychologist or what you think might be wrong with her. Thanks!