Wow, I'm sorry but that employee is very, very ignorant >:(
Like others have said, females can be kept in a sorority, but you need plenty of hiding spots and this does not guarantee that you won't have conflicts. As a first-time fishkeeper, I'd steer away from this option.
That being said, some females and males (one or the other, not both together!) do just fine in a peaceful community tank. I have kept a male betta with a school of corydoras catfish, and this seemed to be a very good combination as the corys are very peaceful bottom dwellers. They are also really fun to watch as they play with each other and scavenge through the sand (they do need a sand substrate because of their sensitive barbels).
I hope this helps!