I think it's, of course, to start of the film in a highly sexy way. But also, to show that she's horny and aroused and going through a sexual awakening. After all that, I think the immediate message is that April is bored, bored, bored, and trapped. And her play time in the shower is something that belongs all to her. I also always thought that she was masturbating in the shower, too, but maybe not. Her relationship with the fiance is a totally unsatisfying sexual relationship for her, hence Perry.
Indeed. I don't think it's a sexual awakening, but showing how unhappy she is with her current life. She is ones of those people who yearn for more in life then just what money can give. And since she is about to get married, that part of her is coming out. Looking at the men, is her wanting for something more then she has.