[pyrnet] new behavior-growling at small dog

[Sherri Artz <SArtz@wiche.edu>]

My 1 year and 2 month old  female spayed  pyr Dumpling has been raised with
two jack russells and a tiny old chihuahua.  She is very playful with them
and never aggressive (She doesn't play with the chihuahua, he dislikes her
very much).  She does growl and act tough sometimes with bones, but still
very much knows her limits.    The 11 year old male chihuahua totally
attacks her and she just wrinkles her nose and backs away.  She has been to
puppy pre-school and puppy kindergarten and really came out of her shell.
She loves other dogs and only ever growled at a husky puppy who literally
was hanging on her leash for 1/4 mile of our walk.  (Don't know who's puppy,
probably a guest in the neighborhood.)  About 3 weeks ago I took her to a
friend's house where there was an aggressive rather small rotty/chow/smaller
dog mix who attacked her.  Dumpling didn't care, she didn't fight back, she
just let him snap away at her.  We broke them up and kept them apart and
took them for a walk and it seemed to work out, although, we never let them
together again.

Then, last night I was visiting the same friend and a very small jack
russell/chihuahua/something else mix male dog (maybe 8 lbs) came over.  The
little guy was adorable a very very sweet.  I had Dumpling on her leash and
ready leave.  Dumpling sniffed the little guy an started to growling in a
very ugly manner and went after him.  I was horrified.  The owner of the
little dog was really not to concerned and she thought I should let Dumpling
off her leash and let them get familiar.  Normally I would have but one nip
and that sweet little guy could have been done.  I really don't think she
would have harmed him, but I wasn't taking any chances.  She loves other
dogs, just loves them, especially bigger ones.  

What could have made her do this?  Is this normal "getting to know you" dog
behavior (it hasn't been for her)?  Can I trust her with small dogs?  She is
excellent with our little dogs and our cats?  My gut feelings tells me if
I'd have left her go, they would have been friends in no time.  She has had
a scuffle or two with our male jack over a toy or bone.  It sounded ugly
they were really mad but they seemed to know not to go to next level.  

Am I over reacting?  Thanks for any advice.

Sherri