My dog growls at other dogs...

I have a 9 month old female Nova Scotia duck tolling retriever.
We picked her from the litter of 8 because she quietly played with a ball while the others climbed on each other at 6 weeks.

We got her into training at 8 weeks and took her to puppy play time at Petco frequently. She did fine until she was about 5 months old. Then she started growling at other puppies. Tried it a few times and had to stop taking her; people don't like their dogs growled at. She still plays well with a sister that lives near us, but rarely see her.

We rarely encounter other dogs, but when we do she smells them, but doesn't seem particularly interested. (she loves all people...)

We had a 16 year old until last month, but pretty much had to keep them apart; the puppy wanted to play and the 16 year old just wanted to be left alone.

Today we took her to a kennel for an interview. Guy has two of his own dogs and boards up to 5 dogs at time. He gives them free run of his house and has two outside runs. (the house was surprisingly well ordered and clean!) Chloe was a bit intimidated by all the dogs and all the noise, but she generally did okay, except she growled twice at a boisterous golden puppy about twice her size. The guy said it wasn't important; the golden was crowding her, and she was telling it to back off. They would work it out on their own.

So, now that you know everything about Chloe...
1) What do you make of her general dislike of dogs? Just a individual characteristic? Keep her away from other dogs? Encourage her to be with other dogs? Take her to a behaviorist?
2) Is she likely to be okay at the kennel we visited today for a week? It will be next March, so she will be a bit more mature and spayed, if that matters.

She is our third Toller and neither of them particularly cared for other dogs either, but we never took the other two to puppy play times.

Chloe may never be a social butterfly but I would think you need to keep her contacts with other dogs going for her own benefit - and yours. It may be that she would benefit from one dog at a time rather than a free for all where she feels overwhelmed. A lot of female dogs are not particularly bothered about other dogs, but they should tolerate a certain amount of interaction, so keep on with that. Has she had a season yet - 9 months and she may probably have a season soon - that can make a bitch a bit moody. If the person who is going to board her is OK with her I don't think there will be a great problem - he sounds as if he understands dogs and should know how to manage her and his group of dogs.

She was in season a month ago. We will have her spayed in early January. She hasn't gained any weight in 2 months, so we figure she is full grown.

Growling doesn't always mean anything negative. Like you mentioned, it is a way dog's communicate "Hey! You're too close! I need space!"

I work at a Boarding Center and we have Doggy Daycare, we see this quite frequently. We normally don't worry about it unless it become more aggressive. You have to allow dogs to work out their problems while still being Alpha (as in you or the HUMAN in the room). We have a resident dog and when I bring my 5 year old dachshund and the resident dog growls at him to let him know he needs space or to say "I'm not in the mood for your invasive sniffing right now!"

Just make sure dogs are always supervised when they're with other dogs.