Thank you for your question!
Prior to even considering another dog I would really recommend having Bonnie assessed by a qualified professional who understands behaviour and works with reward based training.
Dogs like people all have different personalities and your girl sounds like she has a large personal ‘bubble’. She has had her routine turned upside with the move down and adding another dog into the mix can make the situation worse. Dogs are not top dogs or submissive dogs, rather behaviour is fluid and dogs react to other dogs just as people do. You may like someone at first sight or be annoyed by that person.
Bonnie’s tolerance levels for other dogs may be really low or she might be resource guarding space, you or other objects. In the meantime you could try giving Bonnie some enrichment to engage her brain throughout the day and mentally stimulate her. I have an ‘only dog’ at home too and I find Yoshi is so much more engaged when he has food puzzles to figure out or we play games where I hide his toys and he has to find them. Good luck with your girl!
-Dr. Alex Hynes