[PennyO]

Hi everyone, I am going to post again on my 7 month old Yorkie. She has been really timid and friendly since I have had her for the last 2 weeks. However, within this week I started seeing more and more aggressive traits. I don't know if she is now warming up to us and being more of a dog or I am just worrying to much.

Penny hasn't really growled or barked in my presence until yesterday I brought her to work. She fell asleep under my desk and a co worker came by and she woke up and growled and then the growling rumbled. She wasn't showing teeth and actually was still in her sleeping position. I then took her out and had my co worker give her a treat and he pet her no problem.

The same night I went to my mom's house to stay over night and when my mom came home, Penny growled at her too. Same routine I told her no and then really nothing more happened.

Today I brought her to work again and was good in her carrier bag when my boss approached she growled slightly and the barked. I told her NO and she barked...so I flipped her over. I then took her out of the bag and My boss said hi, she approached and she let him pet her. She then was biting her bag after I put her in and this time I said NOOOOO and she looked like she got sad and went in her bag and just slept and all curiosity of exploring the office stopped.

Problem (2 questions).
1. I am having problems with reinforcements, so when I say no to her and she obeys am I suppose to praise her for obeying me? Or leave her alone.
I just was told that they need a lot of positive reinforcements but so this last NO I prolonged the saying and it seemed to traumatize her. My "no's" has usually been just a stern no.

2. Is the barking at strangers normal? It's not non stop she eventually stops and then is friendly but I am scared it might turn aggressive (I had a Maltese that was put to sleep because she bit everyone in site and caused both my mom and I with numerous scars). Penny so far is gentle, I feed her treats and if I take it from her so far (knock on wood) she doesn't care. But I am scared of the growling and barking. Overall she is not a barker at all when we are around except when she is left home alone. But this new thing with her barking at strangers when I brought her to the office last week with no problem. I don't know if she is now familiarized with the territory and just protecting me?
Please help!