Try putting a treat on the other side. Push it a tiny bit open with your hand to see if she'll go the rest of the way through. Ignore the look that says: "Please open it all the way for me you silly human".
It's okay to give her a gentle push on the rump to get her to go through. Once she's gone through a few times, she should get the hang of it. :)
You can help the HubPages community highlight top quality content by ranking this answer up or down.