This, I should think, is akin to her tendency to idealize childhood to an extremely stupid degree. A person who doesn't envy others and isn't sick with the delusion that everyone is having a better time than she is would look at a small child and see someone who lives at the caprice of others. Other people get to decide everything for a child and tend to set her opinion at naught; granted, it is generally done in the child's best interests but the knowledge of being helpless tends to make childhood a time of misery and confusion.
Similarly, Lynn isn't quite aware of the drawbacks to being a man. Leaving aside the dying earlier part, this belief of hers that being a man is a cakewalk because a man doesn't have to be domestic if he doesn't want to is sort of off-base. The reason that comes closest to mind is that most of the things about men that she envies are things that she doesn't question because they make her life easier. It's simpler for her to have John be a poor helper because his being adequate means that she's redundant and must therefore die like all useless things. We thus have her envy being a man because she can't see that he isn't any more free than she is. Then again, Lynn never wants to admit that people are all having pretty much a lousy time of it because if everyone is a victim, no one is.