dont listen to those three people up top.
This is actually very serious.
having an overactive bladder can lead to serious infections and can have her being afraid for her friends to spend the night,or to go to their house.
My sister had this problem and it was a big issue.
It took the longest time for my mother and her to get it under controll.
She had to know that there were ways to prevent it, like no water after dinner, make sure you go to the bath room before bed, and that mom wasn't going to be mad at her, and for a few months she had an alarm clock that woke her up every few hours so she went to the bath room.
And eventually she was able to get up on her own with out the clock.
Besides the over active bladder being the main issue, stress can have a large impact on it. If she's stressed out about it, it can lead to her actually doing it.
Talk to her about it. Let her know that she isn't the only one with this problem. And find a solution to help her cope with it.
It took my sister till she was 16 to finally get it under controll. But she still can't go to bed if she's stressed about anything because she will end up wetting it.
Hope I helped