For some girls, it's hard to say no. They may be so nice, they don't like saying no. Or they may be so shy, they don't like saying no.
To break out of this stage, practice saying no to a stuffed animal. Yes, it sounds stupid, but it works. Use your (or a siblings) stuffed animal, and when your alone in your room, yell, "NO!" Imagine the stuffed animal forces you to go log onto a bad site, or something you know you'd never do. Yell, "NO!" at it.
When you grow the courage, practice with a parent or sibling. Tell your sibling/parent to tell you to do something you wouldn't want to do. Then tell them, "No!". Practice this for a while. At least once or twice a week.
Then, do the same process to a friend. Practice this for a while, too.
As hard work pays off, the next time someone urges you to do something you don't want to, it may come as instinct to just blurt, "No!" or you may feel so brave, you shout it out without hesitating.