She changes

Megan pulled the large, metal door open to get into the changing room. From the sound of it, no one was in there, which was just as well: she had always gotten a little nervous changing in front of other people, even other girls. Her body was a private thing. She found a convenient place to sit, in front of a set of lockers, and started to undress. First came her shoes and socks, then she quickly unbuttoned down her blouse. A quick flick and her bra was unhooked before slipping down onto the tile floor. She stood up just long enough to release the catch of her skirt and push her panties down, then slipped into her swimsuit and got herself properly dressed for a good swim.

Her clothes ended up getting shoved into one of the lockers. She did not bother with a lock, since she didn't have one and there weren't any people there to do anything with them anyway. Then it was back out the door for a quick swim.