Habibi

[Habibi]

Hello, my 2 and a half year female cairn has been sweet and mellow ( believe it or not). But then we went away for two weeks and left her at home with a dog sitter that she loves. When we came back, she had developed an unbelievable, aggressive, protective behavior. The sitter only noticed it once when her husband came to visit. 
Anyone that comes to the house now, to do work, makes her unbelievably aggressive and agitated. She lunges at the window. If I take her outside to meet them she wants to rip their leg off. 
she went after my brothers Jack Russell for 2 days when they came to visit. Only the girl. Not the other dog who is male. 
We don’t understand how this got so out of hand  

NEED HELP DESPERATELY. 
Thank you for any words of wisdom and guidance. 
 

I couldn’t get a pic in. She’s so beautiful!

[bradl]

Welcome, and sorry you are having this issue.

Figuring out what's going on with sudden and substantial behavioral changes often begins at the vet to rule out any health issues that may manifest oddly. It's hard to image an infected tooth (as a random example) resulting in animosity toward a specific individual for instance, but stranger things have happened. 

I can't speak to your specific situation and environment so can only say that in our personal experience the "I will fight you and never back down" permanent grudge match relationships we've encountered have always been between females.  The boys for some reason seem to display a lot of showy bravado and occasional serious scuffles but seem less likely to hold a grudge. Or maybe are more able to accept a lower place in the pecking order while the girls never give up their drive to be Queen as it were.

Hang in there. Keeping your girl busy, occupied, and challenged with activities (walks, obedience, dog sports, hunting if appropriate, games, and exercise of all sorts both physical and mental) go a long way to smoothing out life with an opinionated Cairn.