First you want to train without it. The real only good thing a ecollar is for would be working at a distance away from you. Right now she is too young for both the ecollar and being away from you. You do not want to even worry about off leash I would say until after a year old. I didn't let Hemi go off leash for walks or anything until he was about a year and a half. He had to walk good on leash before he got to walk off leash. Then as far as age. 8-9 months is where I would look at Ecollar if you think you need it. Right now also at this age is critical. You need to do a lot of good and positive training. Train Recall, train leave it, train them all on leash get it drilled into her head. Right now you are building the foundation for the dog you want to have by training the puppy.
You can train a very strong recall without ever even using a ecollar. ecollar without the proper training can actually prove harmful. Suppose she is walking towards something, you zap her and it scares her and she runs off into traffic. You need to train a solid recall.
Hemi loves fireworks for example. I have a good solid recall, you can see in this video. I didn't grabbing the firework. So his recall worked, twice. It can break his attention on anything.
https://vid1251.photobucket.com/album...pssq2kgz3q.mp4
To train recall, you need to choose your word. Then when you say it and the dog comes to you. When you use your recall word you make it the happiest moment ever. Lots of praise and hugs and dancing and treats. Practice, practice, practice. Bring in other people to help. Have them play with a toy, you say the recall word and she should come to you right now and there and give her praise and love and treats and let her go back to playing. Your not out to punish her. This way when you use it and you really need it, it will work.