I know what you mean, and I don't think you're a misogynist. Ideally, it should not strain credulity so much that it bumps us out of the movie. Still, I've seen much worse, so while we're suspending disbelief about a post-apocalyptic hellscape where there's no provision for repairing the generator even though everything else for survival was covered, I'm willing to find the generosity to extend that to the actor's physique, at least in this case.
Edit: I was trying to remember a much worse example. It was so long ago, but I found it! Bridget Fonda in Point of No Return (1993) is the worst casting decision I have ever seen for a "tough girl" role, where she faces off against much bigger men in a variety of situations, including a boxing ring. The trailer alone used to drive me batty - "What do you do when you're most uncomfortable?". Reply from the emaciated, young lady, "I hit". Nope. No you don't.