My dogs are very familiar with my husband and son, but I guarantee you that if one of them were to try to harm me, my dogs would do more than bark, they would be going crazy, snarling, growling, jumping and biting their feet and legs and tearing flesh off them. One of them barks at my hubby when he leans down to kiss me goodbye when he leaves for work. The other one just moves up next to me and watches him, but you can tell he is on alert. They are very protective of me, and that's typical of most all dogs who are with someone most of the time.
In reading some of the possible scenarios, I think I would prefer to believe the most likely, and that is that Susan was abducted in the parking lot. I'm sure LE has checked out the husband, their life together, her friends, and her habits enough that they can be fairly certain she was not killed at home. Likewise, I don't think she would abandon her purse and her credit cards to take off for another life somewhere. Doesn't appear to me that she would have any reason to do that.
As far as people not knowing that a woman is being abused, grown sons would know, if they're in frequent contact. If not by visible signs of bruising, then by how they act around each other, whether she appeared to be afraid of him, was careful of what she says around him, or acted unusually subdued for some reason. I trust Kjac when he says there was nothing as far as her home life that would suggest his dad could have killed his mom. Family knows their family best.