In a book all about gender, Roberta has a better understanding of the subject than most.
Although we learn a lot about Roberta, we're never introduced to her former identity: Robert Muldoon, standout NFL tight-end. You don't get much more stereotypically manly than that. And after her professional football career, despite her delicate "heart of hearts," Roberta will always have a body like a "highly trained rock" (14.136). This makes her ideal bodyguard material for Jenny Fields.
It must've taken a lot of hutzpah for Roberta to come out as transgender—remember, The World According to Garp was published in 1978—but what's worse is that Roberta still doesn't feel completely comfortable since she's been met with skepticism from feminists and men alike.
It's not until later that Roberta realizes her burden can be a gift. She now has "the vanity of a middle-aged man and the anxieties of a middle-aged woman"—a perspective that "is not without its advantages" (19.173). She comes to peace, finally, with all the aspects of her identity. A woman through and through, she no longer concerns herself with society's expectations for who or how she should be, and instead learns to appreciate herself in all her powerhouse, feminine glory.