Barking wll come later... repetition... one day it will all click and come togehter. I had my 6 month old out for first time today and she tongued a few times... but not steady... when they were in check she worked and tongued as if she knew what ir was all about... but once they pushed again she was more intent on running... it will all come together.
Have alot of patience with her also. Keep the training short. 3 1/2 months old is very young. and as she grows and matures she will start using her mouth and sticking to the track. Starting pups is one of my favorite parts of beagles.