Aimee...........you are not a bad person. There are many things I have said to my dogs in exhaustion and frustration that I NEVER meant. We are all human and we all do the best we can at any given point in time.
As far as Marla being happy? She looks pretty dang happy to me in the photos.
I do know a little bit of how you feel about the guilt. I will never forgive myself for Bones getting hurt. He never deserved what happened to him. Still...........it is over and done. I do my best to let go of the guilt, but every now and again it rears it's ugly head. I understand.