First figure out what exactly is making intimacy difficult. Is it sheer aesthetics? Is your fear that this person is living an unhealthy lifestyle distracting you? What is the real issue here? She is a grown woman who is allowed to care for herself and her body however she sees fit. Through observations, you have made certain inferences, but if you haven't really had conversations with her about her views on what constitutes fitness, you're just supposing that something is awry.
She's absolutely stunning but I'm not sure if she does have a masculine side, so am I gonna fancy her? In this moment, I don't feel like I do. Sh*t,
If it's your job to figure out when to share this, it's also a partner's job to figure out when to ask. Wanting kids isn't like monogamy or working for a living, where until instructed otherwise people can basically assume that's your plan. More people than ever are deciding they don't want kids. The fact that you're one of them is not shocking, confronting or even especially unusual.