You've gotten a lot of good advice on working a bird, and it demonstrates my one rule of hunting; there is no "always" or "never" in hunting.
I'll offer a suggestion though. Whenever you see hens without a gobbler, try to work them. If they're quiet, whines, SOFT clucks and SOFT purrs are usually best. If they're loud and aggressive, usually your best bet is to perfectly mimic them, but even then I usually start with the soft stuff. When you get to the point you can call up hens on a fairly consistent basis, you'll get better at calling gobblers whether alone or in the company of hens.
Basically, use every opportunity possible to learn to call hens. Heck, every now and then a gobbler will show up to the party too.