Join Date: Aug 2011
Location: San Bernardino, CA
A good rule of thumb when you're keeping a community tank is one gallon of water for every inch of fish. You want to think ahead for when your fishes grow, as most fish do, and make sure your accommodations are right for them. Also, keep in mind that female bettas can be just as aggressive toward other brightly colored fish as male bettas are, and guppies usually aren't the best tank mates for bettas at all (i know from personal experience, sadly).
If you want to put your female betta in a tank with tank mates, I would suggest something more along the lines of mollies, or another non-aggressive community fish. I have personally had tanks where I've had gourami in with my bettas and they co-exist nicely, but bear in mind that gourami are semi-aggressive.
Make sure you have plenty of plants and hide-aways for your fishies, as female bettas can be extremely territorial. (Or you could end up with a nice docile one, which I've also had the pleasure of having. But the general rule of thumb with bettas is be prepared for aggression and have a back up plan).