aggressive around puppies

Hi, I'm a new Pet of the Day poster. My dog Georgia is an absolutely wonderful, 60-pound, chocolate lab, who just celebrated her year and a half birthday last week. She's great with people, good/great with commands, not possessive with toys, playful, great at retrieving sticks and balls, and very gentle with her mouth around people. All things considered, Georgia is wonderful.
Where she is not always so great is with other dogs. She plays wonderfully with some dogs (typically dogs her size, age, and disposition), but occassionally she can be nasty to older dogs, young puppies, very hyper dogs, and shepherds and huskies. I think this behavior is particularly pronounced when she (or the other dog) is leashed.
Minutes ago, Georgia met a really cute 12 week old lab puppy on the street. Both dogs were leashed. As I said hello to the new dog owner, Georgia showed her teeth to the puppy and then lunged forward, causing the little pup to squeal. I don't know if Georgia would actually hurt the puppy; she has a really soft lab play bite, but she didn't act like she was playing. This is not the first time she's been aggressive with a puppy, and I really don't like seeing her behave this way.
As for Georgia's background... Between her breeder and us, Georgia spent a week and a half with another family (which belatedly decided that they were unready for a dog; we rescued her from the name Chanel). As such, we never met the breeder, so we do not know the disposition of her parents. Georgia was a great puppy from the minute she joined us (excluding her unstoppable fondness for eating poop, but I'll save that for another day). She did puppy obedience class, and did fine. As a puppy, she was a rough player and wouldn't back down to an aggressive dog, but she herself didn't really cross the line. She used to attend doggie day care a few times a week, so she has been socialized from a pretty young age. She spends half her time in the country and half the time in New York City (where she plays off-leash in Central Park each morning), so she has the opportunity to do plenty of running and socializing.
I'm just concerned about this new aggressiveness, especially with puppies. I'd love any thoughts about what's bringing out this unprovoked nastiness in Georgia and what I can do to thwart it. Thanks!

How terribly scary! I have no advice or explanation, but know that others will chime in.

Maybe she somehow thinks she is protecting you or not wanting other dogs to be near you, you said she didnt act mean to the puppy until you came up to greet the new dog owner?

My Rott is friendly with all dogs but when our neigbors (Boxer) dog is on the other side of the fence and I go to pet him he gets ferocious with the Boxer, but... then the dog comes over to play and he is frollicking with him, the only time he acts that way is when the dog is on the other side of the fence ... go figure.
Sorry i wasnt of much help

Oh and he does the same thing with the Danes behind our yard, only when i come to the fence he gets nasty to the other dogs, when i go away he is friendly again. And he only does this when they are behind fences, so maybe that is somewhat similar to the other dogs in your situation being on leash.

Gonzo has issues with hyper dogs and puppies, too. He's never snarled as far as I've seen, but he growls and turns away from them. I do think it's partly a dominance thing - demanding respect from a younger dog that they see as unpredictable - AND she probably knows puppies are reckless, so when she's on-leash she feels attached to you and doesn't want the hyper reckless puppy to bother you or her. If this really concerns you, try to find a good behaviorist to talk to. Since this is the time in Georgia's life when she is actually showing her real personality and maturing, this probably isn't a NEW behavior as much as it is a behavior that was hidden before by being a puppy herself.

I can't figure out the older dogs, shepherds, and husky annoyance. My dog actually loves basically every older dog, shepherd, and especially Husky that he meets... because they tend to be nicer dogs when playing, and my BC plays exactly like a Husky. Huskies and Shepherds have waaay different play styles from Labs, so that might be an issue with her. Labs tend to body-slam and chase (in my experience), and Huskies are more wrestly and such. Gonzo is actually Lab-a-phobic :) probably because he really dislikes their play styles. It just shows you that all dogs are different and have different likes and dislikes!! She could've also had traumatic experiences with a Shepherd or a Husky (pretty similar breeds in some ways, so she might just relate the two breeds as one) while she was in daycare - Gonzo has been attacked by a Black Lab and a Rottie, and now he still vehemently dislikes both breeds in most cases, while he loves most other dogs. The older dog thing, could very well be dominance. A lot of young dominant dogs go out of their way to show off to older dogs, especially since older dogs are much slower and weaker than a young pup. She probably likes dogs her size and age because she does not feel threatened by them.

^_~ these are my ideas anyway, having my own breed-biased pup. I am not a professional at all, so seeing a behaviorist would be a good idea! I'd try to arrange plenty of one-on-one socializing with slightly younger dogs, on very loose or dropped leads (so that in case she gets too overwhelmed you can just grab her lead). I'd try moving from slightly younger dogs, to a few months younger, and make every experience she has with or around a puppy very positive and brief. You really can't expect her to lover EVERY dog (although Labs can be notorious for this, it doesn't apply to all of them)... just like you don't love every person you meet. Good luck! And, we'd love some pics of Georgia! She sounds like a sweet Labbie girl ;)

Thanks for the thoughts. Maybe a doggie therapist is in order; I'd just never be able to admit it to my family!
Georgia is down meeting her doggie-in-laws right now: an unpleasant Jack Russell, and a wonderful (though old and blind) Golden Retriever. My wife reports that the Jack Russell snarls and snaps at Georgia, who seems to be avoiding confrontations as best as possible. She's a bit intrigued by the old, blind Golden, and my wife reports that Georgia is in the (figurative) doghouse right now for mounting her older, unsuspecting doggie-in-law.
So a little dominant behavior, but we'll get to the bottom of it... :rolleyes:
Hopefully I can add a picture of Georgia sometime this weekend.

Georgia sounds lovely! Mika (my labx) doesn't do well with large black dogs, hyper dogs, huskies or akita's if they all bug her when we are at the doggie park. I usually can whistle/call her away before she snaps at them, but often she'll just give them one snap and it's all over, she walks away. When she's on a leash she'll really have a go at any other dog. My other dog gets on fine with any other dog, but also goes nuts thru the fence or while on a leash. Crazy animals!