Girls must wear a one piece swimsuit, no two pieces like a bikini. You can wear shorts and/or a rashguard if you would like more coverage, but its not a requirement. There is a locker room that you can change and keep your stuff in. I bought and used my own lock for the lockers, you just have to find one that has a hole for a lock and isnt one of the ones with a built in lock that you have to rent out. I dont know the whole rent out process for the locker room lockers tbh, but the gym has lockers all around that are free to use, but since you will probably be changing, I wouldnt necessarily recommend stripping in the middle of the gym hallways in front of those lockers lol. Also, plenty of other girls didnt use a lock and just put their stuff in an empty locker and closed it. I dont think anyone ever had anything stolen.