I told her she couldn't ride the roller coaster because she wasn't pretty enough
Why on earth would you say that to her?
Because I'm a mean person.
There doesn't seem to be any good reason for what you said. It's not okay to call people ugly. If you want to maintain friendships and relationships, you should be nicer.
Does it matter?
I just think you shouldn't be so mean to people, attacking people's looks is pretty low.