Hello M.
I've been around dogs my whole life. I'm 43 and having a family with two girls (8+5)and two dogs. Our old one is a middle size Schnauzer mix and our young one is a almoust 3 years old black Lab (mix?). We got her from an animal shelter with 3 months and she fits perfectly in the family. Of course, she tried starting with age 7/8 months to find out, who's the boss in the family. I'm glad, she never showed up some agressiv behavior. Even my old dog (around 12 1/2) had never showing up like this. But, he knows how to tell the girls when it is to much for him. Then he growls a little bit too, but it's only a kind of breeding, he never would bite, he never tried.
My commandation for your dog: Bring her to "mens best friend". We had our Lab over there, for the normal 2 weeks training, and our doggie girl is now a great behavior dog. She is foolowing all our commandos very easely and her character is unbelievable lovely. She is friendly to all children (I take her often with me to school) and distrustful to strange people at our house door. I know, a lot of people say, do not go to "mens best friend", but we got a great education for our dog there. And all the people who I talked to, during this time and between our group lessons love this place. So like we.You gave a puppy a home because you love it. So try this great dog place, and I'm pretty sure, they can help you.
Wish you the best for your family. E.