Looking for advice.

I have a 7 month old terrier/mutt her name is Carly. I adopted her at the age of 13 weeks. Very soon after adopting Carly I started noticing that she was throwing crazy fits in her crate but only when we would leave the room or leave the house. If you are in the room she's just fine. So I called the rescue group to find out how she was behaving in their care. That's when I found out she had already been in 6 homes but other than that they didn't know much more. Sure, I don't believe that, but she's my dog now and I took it for what it was worth and started googling for info about her behavior. That's how I stumbled upon the wonderful Leerburg site. From what I can tell at this age is that it is no longer puppy behavior but a mild to moderate separation anxiety. I've searched and read as much info from here and she has made progress. She's gone from 20 minute fits of barking, howling, whining, biting and scratching at the crate once we leave the house to now I can leave and depending on how much exercise I have given her 95% of the time I might get a bark or two. If she's not tired it will last a bit longer. I'm fine with that because I see progress with age, exercise and consistency. Here is my issue. When I return home, the moment she hears the garage open or a car door close she starts the same crazy barking she used to do when we would leave. How in the world do I correct this? I've tried just waiting her out by not entering the house until she's quiet but I'm not seeing any progress.

How long have you been trying to wait her out? Do you let her out the minute you walk in?

Honestly at this point I've been more concerned about the leaving part and her behavior in the crate through out the day which I monitor via iPad to iPhone. So once I return home and the barking starts I wait till I get about 5 maybe 10 seconds of silence before entering. I can tell when the bark goes from frantic, hey your home and I thought you would never return to, ok I know this will get me nothing so I might as well be quiet. At this point she goes in her crate 20 minutes before leave and comes out 20 minutes after returning assuming she is calm. At this point she has never been left more that 5 hours straight but most of the time it's closer to 3 1/2 hrs.

And when you say how long, do you mean each particular return home or how long in general has this behavior been tolerated?