Aww crap well I've been chastised for being too hard on new members..so this time I'll ask questions first.
I'm assuming that the usual dog to dog intro was done, neutral ground dogs meet and all goes well? The new dog comes into the home and is "given" almost immediately free access to all the resources, free roaming of the house, food, water the yard ,toys etc?
You may or may not have noticed or paid attention to who goes out the door first, gets petted first and who's allowed on the furniture (if that's the rule of the house).
And dominance doesn't "really" rear it',s head till the dog reaches maturity somewhere in the 18 to 30 month range. And dog ages from rescues are educated guesses at best.
Guess that's enough..so how did I do?
You brought up some good points. Especially, who she allows to go first out the door, or on the couch, etc. And the maturity age. Many dog's personalities/temperaments completely change when they reach 2years old... and not always in a good way!
But I still think Carabby needs the advice of a good trainer who can evaluate the two dogs together - put them all on the right path to becoming a happy household. A good trainer will mention those things too... and other things. It's basically the essence of NILIF training technique (Nothing in Life is Free). When behavior is good, they have access to resources. When behavior is not appreciated, the resources are removed (ie: access to the couch).
It doesn't look like "going it alone" is working for them. I'd hate to see this escalate into a bloodly mess. It's always so much harder to fix if you leave it for too long hoping it will work itself out on it's own.