I would work on building focus on walks and redirection before I would resort to use of an e-collar. You've barely had this dog for any length of time... give her a chance to learn and give yourself a chance to understand her.
A GREAT book on leash reactivity, if you are interested:
I feel the problem often times with issues like this, is a lack of creativity on the handler's part with their own personal thinking combo'd with a lack in understanding what the dog is feeling at the time of a reaction. Leash reactivity is usually rooted in over stimulation and frustration... neither
of which are impossible things to worth through without ladling on the positive punishment.