My Dog Is A 10 Year Old Dobie/Shephard She Has

My dog is a 10 year old Dobie/Shephard she has developed the fear of being left, last year I had to start boarding her about every 2 to 3 months for about 8 days each time. Each time her reluctance to get in the car has grown. She now has to be forced to get in the car for any reason. It's not the car because prior to that the car was never an issue, it's not the boarders once she is there she is fine, and they are an excellent boarder and are there 24/7. We have already tried Trazoden 100 mg she weighs 75 lbs. it did not work. Today Xanax was prescribed 1 mg to be used for each episode. My question is how well does Xanax work for a case like this?