After four months of living with my best friend, who happens to be a lady, I am extremely confident that they do fart and it does smell. They may deny this, even immediately after shifting their body to better distribute the gasses, and they may even giggle while denying the existence of a fart, but there exists at least one girl who does fart.
I don't really want to go searching for evidence that she poops, though. I'll leave that one up to you.