I was wondering if it is her pelvic bone. You may want to use a large needless syringe to irrigate her vent after she poops. More to keep the cut area clean. You could even spray it with vetricyn. I was thinking of way to keep her lined up and in place and the only thing I can think of is small butterfly bandages. They sometimes use them on people when stiches aren't really needed but the wound needs to stay closed. There should be enough skin around her vent area to place one or two and keep everything together. Part of what I see in the video does look like it goes inside... I'd push it back in and stick it closed. You could give her stiches but that sounds horribly painful.