New stray pup

[Scorpionstar]

Hi there,
one morning when I went to walk my other dogs I opened the back door and found a Labrador X puppy with no ID just sitting there. She just greeted my other dogs and wandered into the house. I gave her some food and water which she very eager took. I called the police, dog warden and the ISPCA and let them know that the pup was at my house and they should send the owner to me. Six days later I called the above again and I was told that nobody had come forward and I could either take the puppy on myself or transfer it over to the dogwarden where her life would have been limited for another five days. So I decided to keep her. I gave her the usual first treatments of flea/worm and a good wash, bought her a new leash, etc.

She is a very fast learner and mirror image most what my other dogs do - all of them are command trained. However she is a very quiet girl, to quiet for my liking. I do have the feeling that there is something not right with her. She is mostly asleep and when I did some sound exercises like clicking with fingers, etc, and her reactions are either very slow or not present at all towards it. What do you think?. I also try to determine her age which isn't easy due to the fact that she is almost as tall as a Sheep dog or Blue Merle. How can I find out what approx. age she is?

Help towards answers would be very much appreciated, thanks.