Elizabeth doesn't know precisely how she wound up in Equestria. All she knows is that she's now living in what appears to be a real-life version of a cartoon she watched as a little kid. And she's the only human there.
She doesn't really mind, herself. She's made good friends here, and found surprisingly satisfying employment as a woodworker. Her libido is another matter, though.
After six months on a world totally devoid of human men she might share an evening with, she's desperate enough to try a stallion instead. Big Macintosh is a friend, after all, and seems to have the afternoon to himself...