Need HELP ASAP! Agressive JRT

Hi I am new to this forum and come asking for some help/advice.
I have a 8yr old JRT, Kanga who has been my best buddy and has got me through some rough times over the years. When I first got her she was only 6 weeks old and I knew she was too young to leave her mom but the lady I got her from said that the mom was a new mom and wasn't taking good care of them. So I took her home where my ex and I already had a 1yr JRT, Kali who instantly became an adoptive mom to Kanga and they were best friends. Until about a year and a half later when we were getting ready to leave for the day all the sudden Kanga ran to Kali and attacked her. Kali would only cry and not fight back. This was the first of many unforseen attacks by Kanga, she would even go after our cat. It got to the point where we could never have them in the same room and I never trusted Kanga again. We took her to the vet and there is no "medical" reason for the attacks. And we took her to some obedience training but nothing worked. Our trainer said it was because we had 2 unspayed JRT which was a bad combo. So we even got them both spayed. Still nothing changed with Kanga..and Kali eventually wanted nothing to do with Kanga. Eventually my ex and I broke up and he took Kali and I took Kanga.
I kept her out of situations where she might attack another dog. And for 5 years we were good with the exception of one or two incidiences where it wasn't obvious that she was the attacker or not.
Now my boyfriend and I moved in together a few months ago and about 2 months ago we got a male Boxer puppy, Oscar. I was nervous about how Kanga would react but hopeful that they would get along. And they did...she played with him, licked him and even shared her toys. For the last two months they have been great!! Then yesterday for not apparent reason Kanga attcked Oscar and wouldn't let go. I remebered hearing about if you throw water on them the dog will let go...so as I ran to get water my boyfriend was trying to get Kanga to let go. I threw the water on the dogs and Kanga let go....I picked her up and put her in her kennel and went to check on Oscar who actually litterally crapped himself during the attack. He has a cut on his ear and is shaken up but thankfully ok. We kept them sepearted for the rest of the evening and they sleep in kennels at night. Then this morning my boyfriend let them out as usual to go outside to pee and within 10 sec Kanaga attacked Oscar again. I had a glass of water on my night stand which I threw on them and so it was over fast but now I don't trust her again. I don't know what to do. I'm at the point of considering having her put down...which absoutely brakes my heart and makes me sick to my stomach but I'm jsut so scared that she will start attacking again and hurt or worse yet kill another animal or a child. She is a great dog besides these random attacks.
Can anyone recommed a "behaviour specialist" or anything?? Or has anyone been through something like this before??
Sorry it was so long..but its been a long road.

I should mention that I live in Calgary...if anyone knows of any good behavior/aggression specialists in the area

I am sorry that you are going through this...

Although I do not like to label breeds, being a fearless and tenacious hunter, JRT's are often reactive/aggressive to other dogs, especially when they are in tact and of the same sex.
At this age and given the incidents, its probable that even with intense, daily desensitization and counter-conditioning, you will always have to do a fair bit of management.
Given Kanga's history, I would never leave her unsupervised with other dogs (or small animals/people for that matter).

Then this morning my boyfriend let them out as usual to go outside to pee and within 10 sec Kanaga attacked Oscar again.
You know her history iffy and less than 12hrs ago she attacked a puppy but they are let loose together anyway? That's a mistake that I hope won't happen again.

Before I can offer any good suggestions (aside from finding a good positive reinforcement behaviourist) you will have to give a bit more background on Kanga:
How much socialization has she had in the last few years? And what kind of socialization (on-leash, off-leash etc...)?
What is her bite history (is this the first time she's drawn blood)?
How does she act when she sees dogs close by and far away? Does she socialize well with any dogs on a regular basis??
How much mental and physical stimulation does she get?
Does she know basic obedience commands?

I also think its extremely important that Oscar starts going through doggy socialization bootcamp (classes, parks, play dates with dogs that are bombproof).... After being attacked, you really want to get as many positive dog encounters behind Oscar so he doesn't start to have issues.

I'm at the point of considering having her put down...
I hope you will not take this route. You said yourself, Kanga is a great dog aside from these random attacks... First of all, they are NOT random... I guarantee that Kange is giving off signals - you need to learn to read her body language so you can see how she is going to act and intervene if necessary (before things excalate). Secondly, you managed Kanga for 5 years with major incident, you can do this! Thirdly, you have a commitment to Kanga, don't give up before you've tried.:grouphug:

Brenda Aloff, Ali Brown, Emma Parsons, Jean Donaldson, Patricia McConnell all have excellent books/dvd's on dog aggression/reactivity/body language.

"Can anyone recommed a "behaviour specialist" or anything?? Or has anyone been through something like this before??
Sorry it was so long..but its been a long road. "

Calgary aggression specialist: JC. St Louis. He is in the yellow pages. He has 20-some yrs experience, is court certified and has handled police dogs. He helped us greatly.. Also, you can try Canine Country (country Hills blvd), Joanne there is good. And at Tail Blazers in Arbour Lake there is a woman who works with aggressive dogs. We havent used her, but her card if on the counter and we chatted a few times. :) Experience is key, you dont want to do anything wrong with an aggressive dog.

Id suggest dog daycare 3-4x month once he can be trusted, just to keep up the socialisation..like lissa said too, parks, etc..keep the good momentum going once you get there! It IS possible to correct this! Try a decent trainer first, and keep posting!
Good luck!

In the meantime... perhaps a muzzle?