Sometime aggressive JR puppy

Question
I have a 17 week old female Jack Russell. We have had her since 14 weeks, she was well socialized with other dogs and puppies but seeing as she had no injections we had to wait to take her out. When we did she was ok with dogs that were at a distance but when they came nose to nose she would growl,snap and bark. she is such a placid dog with humans and just in general she is so laid back. She doesn't even bother with our indoor Guinea pigs! will she become more used to dogs? is there anything we can? My sister is coming down with her 17 week old springer and we don't want her to go for her, or would this help her? Please help. Thank you

Answer
Hi Kiera,
Congrats on the new puppy!
It's important to start right away and train her NOT to be aggressive to other dogs. You can do this by giving her LOTS of exposure to other dogs as much as you can. Take her to the parks, take her to the pet stores, keep introducing more and more dogs into her life.
If and when she starts growling at another dog, you have to IMMEDIATELY correct the behavior by snapping her out of that mode of thinking. Cesar Milan, THE DOG WHISPERER uses a great technique of combining a noise command (he uses the sound PSST) and a firm touch on the pups body. Basically what you are doing is getting her mind OFF the dog and aggression, and breaking her concentration on them.
You have to do this each and every time she shows any aggression and I have seen it work first hand. You can watch Cesar on the National Geographic Channel on Friday nights and see the technique in action, it's great!  
Best of luck with the pup and the training...!! Be the boss!!