Jack Russell attitude problem

Hi Guys

I generally only read threads on this forum but I am in desperate need of some advice.

I have a 2 year old Jack Russell bitch (speyed). She is a shocker when it comes to other dogs, her whole life she has growled and snapped at other dogs. She grew up around 3-4 big dogs who tended to ignore her, and because we were in the country it was never a problem. However we are now in town for a few months and it has gotten pretty embarrassing. Last week she attacked a pitty/mastiff looking thing and today it was a poodle/spaniel. No hello or bum sniffing first, just straight into them.

I have an idea how to fix her but am keen for advice.

My idea has two parts. Part 1 I will muzzle her and take her to as many doggie places as possible, praise her for no reaction and growl her for negative reactions.

Part 2 involves an e collar.

All advice considered, please help.

Thanks

Allan