Dogs do not do things out of spite ie holding back pee and poop to use it at a later time. A dog's brain does not work in this manner. If you are taking her out to potty and she squats as though she is peeing then she needs to be seen by a vet for further evaluation.
As for her sneaking off~if she is doing this then you are allowing it to occur. There is no reason why you cannot keep her on a leash at your feet while you are studying.
You said that she shows teeth while on the couch with a bone. If this is happening you are allowing this as well. Do not allow her onto the couch if she behaves this way.
If she is biting and showing teeth, you need to keep her under control w/o hitting her and a good way to do this is to once again~keep a leash and harness on her and redirect her.
Finally, LadyJane is a very knowledgeable member of the YT community and insinuating that she is a bitch is totally unacceptable. She has dealt this more abused dogs in rescue than you are years old. Show a little respect!
__________________ “Never argue with a fool, onlookers may not be able to tell the difference.”  Mark Twain |