Thanks for your help, everyone. Amber ate a treat (she must have been sitting on it!) after about 40 minutes and finally let us back in to the living room! Since then, she has been a bit growly, but Mark has firmly told her 'no' and she has backed down. She's now sleeping in her bed.
I spoke to Cynthia at NESSR, where she came from, who is very supportive. We are going to see how things go. This is Amber's third home, but no aggression has been mentioned before, however she has always lived with other dogs, so perhaps she is trying it on now she is 'top dog' or in fact, the only dog? We are going to be very clear about her boundaries and get a crate or stair gate to she has 'time out' if necessary.
I absolutely do not want to give up on her, neither does Mark, as we are so attached to her already. I am sure we can get this right. It's still early days and tomorrow I go back to work after the Christmas break, so some sort of routine will be established again.
I've also emailed two behaviourists, one has quoted me £850.00 + travelling expenses, for two sessions, which is way beyond our budget! I'll look for others in the East Midlands area.
I'll keep you posted.
This site is great, it's kept me sane this past week or so. I can't express how grateful I am to you all for taking the time to help us. 'Thank you' just doesn't cover it!
Lisa