[sandrag86]

Hello all, hope everyone is having a great Friday so far. I just had a quick question. Was looking for some advice and some tips as to what I should do.

I brought my Lou'e home about 2 weeks ago and he has been doing amazingly well...he listening, is easy to train and is just the move lovable puppy (he turns 12 weeks this Tuesday).
I live in the basement apartment of my boyfriend's Mom's house.
Upstairs, she lives there with her dog - a 9 year old Jack Russel Terrier that is prone to seizures, her name is Nellie.
Nellie is overweight (built like a tank, I say) but she is quick, LOUD, and she occasionally likes to kill things in the background (squirrels and such).

When I brought Lou'e home, they met. Of course I did not put little Lou down, but we let Nellie smell him and vice versa. This was done a couple of times (almost had a mini heart attack).
Well, now Lou'e is becoming more laid back...
When I come home he begins to bark - or sometimes even when he is playing he occasionally barks...this leads Nellie to bark incessantly upstairs.
Today though when I was leaving my apartment and leaving I heard Nellie growling.
Nellie is not downstairs at the door or anything, she just lays in her bed and barks/growls.
This freaks me out because I really don't want anything to happen to Lou'e and he is the size a bunny right now.

What do you think is Nellie's problem?
She was fine for a bit and now seems sort of put off. When I call to Nellie she wags her tail and such and she isn't allowed downstairs. Should I have her meet Lou'e again downstairs where she isn't "in her element"? Should I wait?
Is it jealousy?

Was wondering if anyone could offer any tips or advice?
Thanks very much.

PS. Nellie hasn't been socialized.
She never goes for walks and usually doesn't like other dogs.
I did have a 15 year old cat that lived in the apartment and she never touched him, to be quite honest, I think she was afraid of him. But you know how cats are, they rule whatever house they enter, lol.