They mean get your parents to buy you a new divider, it's very important. The girl needs her own space and fast! Being in the water with the boys will make the male with her try to constantly mate with her, which will tire her out and she will fight back, and when bettas fight it gets nasty and they could kill each other. Bettas also release hormones into the water, you could end up with a worse situation where the other male jumps the divider and all three are on one side..YIKES!
Separate them somehow, even if she has to stay in a vase until you can get her a new home/new divider!