Damn it !! I checked and I was wrong, XD.
I only really know Flower and Dream's members. So don't trust me at all.
I think she is Yuzuna Takebe.
http://www.generasia.com/wiki/Takebe_Yuzuna
Check the picture on generasia, is the same girl ?
Honestly, I'm not sure because I don't know the bunny members. I didn't know she was a vocalist.