I didn't think she was sexualized for the audience either. There was a pretty audible "ewww" coming from the audience during the pharmacist scene both times I saw the movie, and it was meant to get that reaction. She wasn't trying to be sexy for the audience, she was exploiting the fact that she knew the pharmacist was a creep. And he was.
And I don't think the boys watching her sunbathing was sexualized for the audience. It was meant to be from the boys' perspective, and they were 13-year-old boys, they can't help it at that age, it's just what they do. The scene wasn't trying to show how "sexy" Bev was, it was showing the boys' reaction to seeing her sunbathing, and I thought it was pretty typical of their age, and actually kind of sweet (not that they should leer at another girl, but that they couldn't help themselves).
Both times I saw it, I heard a few women laugh at the scene when she's trying to figure out the tampon aisle, and trying not to let the other girls see her. I think it was a moment every teenage girl went through at some point or another.
I didn't love the whole bit where she needed rescuing at the end, but I thought she was overall a great character. My crowd cheered when she decked her father with the top of the toilet tank.
There's a good article about Beverly here that I think sums her up pretty well:
IT TELLS A STORY ABOUT THE VERY REAL FEARS OF WOMANHOOD