My 18month old jack russell

Question
Hi,
About 6 months ago i rescued a jack russell cross chihuahua from a lady who didnt know how to look after dogs.

Roxy (the dog) Is the most loving little girl ever, so clever and sensitive, she doesnt go near other animals, but has a best friend tilly (another jack) and ever since they first met they do everything together, this afternoon after our christmas dinner there was quite a lot of people on the front room cuddled up on the sofa watching telly. tilly was down on the floor smelling something so roxy jumped down to have a smell too, out of nowhere they both started to fight viciously! i have never been so scared my friends dad and brother had to physically pull them apart because roxy had her jaw locked around tilly's head.

They have both come off bad and battered, After they had been pulled apart roxy got put outside as tilly was bleeding, after trying to calm myself down i went outside to see roxy as she seemed to have calmed down. i brought her in the kitchen where there was light to check her over she had been bitten too by tilly but then tilly came running in the kitchen and they both tried to bite each other again so i took roxy upstairs and locked the door where i was trying to calm her down.

out of nowhere she bit my hand, now i have to explain that i have had jacks all my life and roxy is the most quite timid and sensitive one i have ever had, she will gladly just sit next to bunny rabbits and cats and not flinch or try and chase them when they walk off. she has been trained to walk off the lead, she doesnt chase anything that moves and isnt fased by other dogs when she is out walking, if another dog comes up to her when we are out she just carrys on walking as if the dog hadnt even been near her.

so this was extremely out of character for roxy and i am really scared now as she has been my lifeline over the past 6 months.

the christmas day was very busy and loud so i understand they would have been wound up and wanting attention as they were not getting as much as normal!

I really dont understand why this has happened and its now made me nervous of going near my own dog and i am wondering if you could help me try to work out why it happened and how to stop it happening again before i take her to the vets when they open after the christmas break, I am going to have her checked for any brain problems or maybe pressure on the brain.

roxy has never ever done anything like this before and i am really upset about it, after she bit me she was locked in her cage for over a hour and has seemed to gone back to her lovely self. but still its terrifying

help me please :(

Answer
Dear Kelly,
First off- Merry Christmas. In spite of this.
When you have 2 terriers sniffing the same scent in a crowded situation with a splash of Chihuahua thrown in, all's fair. Unfortunately this is not uncommon. The best thing to do is avoid the set up. As difficult as that may sound it's up to you as the pack leader. Fear is the motivator here and the rest can just be the breed. Chihuahua's are known to have that trait.
Pulling them apart can be extremely dangerous for all involved because in the throws of adrenaline they revert to base instinct. I can tell you I would not have put my hands anywhere near them. You didn't need to calm her down which was your mistake. You could have just put them both in time out. Equal and same treatment they could both see.
This may happen again. Most likely will. They tend to make more noise than anything and if you get involved it takes on a whole new meaning- free for all! Yup, there will be blood. Better theirs than yours. If they continue to have these tete tet's you will have to have some one come in and evaluate the situation or just keep them apart. You don't say how old they are but older dogs tend to get more aggressive f they don't get their way.
It sounds like you really understand what happened, you just aren't prepared to deal with the consequences. Try not to get overly emotional but calmly figure out how to remove them from the situation and just separate them within eye distance so they both know you are the boss. To remove and rewards the bad behavior by secluding yourself with the dog will just cause more angst.
Get in touch with a trainer That would be more practical since seeing you in action is the most important part of the puzzle. You must however finding someone who deals in terriers. Check their credentials and ask to speak to other clients and look at pictures. Meanwhile shorter visits are appropriate until you feel more comfortable with the situation.
But speak with a trainer and avoid that kind of situation in the future at least until you are more confident.
Happy New Year!