Then the best solution is called a prickly pear, or a speculum. Either can be inserted in her ass and expanded to the needed size without completely destroying her. They'll teach the little bitch to relax, yet leave her with bowel control. I don't currently have one, but can get one on Amazon, and will do so at the right point in her training cycle.
Now, for the main two questions:
1. When am I going to begin training her?
2. What is your email address, so I can send my IRL address?