I just want to give you a bit of a warning is all then.
Female Betta's can be just as aggressive as males, although males tend to do most of the "killing". You'll also have to watch out for breeding, during that time the male can get extremely aggressive. Many breeders have lost their spawning pair due to this. There's also a possibility that she could become Egg-bound if she is not in tip-top shape.
I just wanted to comment on that so you don't end up with some dead fish is all. And as many of us have experienced here, taking advice from a petstore is generally a bad idea as most of them just want to make money so they'll tell you anything.
Also, yes Betta's can be in communities, however they are more likely to be nipped, especially by Barbs so just watch out for any aggression coming from your Barbs.
A heavily planted tank would be alright for a Betta in a community but, I personally, still wouldn't risk it. But if you feed adamant that this is going to work out, then go for it, I just wanted to let you know is all