As a trainer, I would like to offer a bit of advice. If you would like more, please do let me know...

First off, how long have you had this girl? I'm sure the anxiety problem stemmed from the previous owner HOWEVER it is only getting worse with you. Now that she is out of her old home, which was her comfort zone, she is more insecure. In her mind, she MUST be with you. After all, when her owners left her one time, they left her for good. Dogs do not understand why they are misplaced and this is where many behaviors stem from.

I agree with KYS, also. When you are going to leave, do not say good-bye to her. Just discreetly leave. This way, it is not exciting when you leave. When you come home, do the same. Put all of your stuff down and when she calms down, a few minutes later, calmly pet her. Don't get all excited, just act normal. The more excited you get, the worse her anxiety will be.

Make sure she is getting enough physical and mental stimulation during the day. This can help relax her too.