Could we have some pics of your betta?
How did you determine her gender? was it on the bowl you bought her in? Sometimes females are actually males called plakats...just thought maybe it'd be a good idea to have a good clear pic, so we can assure you she is indeed female.
As far as tankmates, many of the experienced betta owners on here have betta "sororities", which is a school of female bettas...usually 6 or more...and they need at least 10 gallons. I think most people here would recommend continuing to learn about your first girl before attempting a sorority, as they can be stressful and difficult to handle =)
As far as a male and a female together, thats a HUGE nono...bettas are solitary creatures, and males are SUPER aggressive and will attack any other bettas.
As far as other tankmates, plenty of people have different kinds of shrimp and snails, and there are some other species of fish that are okay with bettas, however the tank should be much larger if you wish to house other species and again, many here would suggest you learn as much as possible about and get used to your original betta first. You might find that you enjoy having the one! Bettas are absolutely packed with personality, and you can have quite a relationship with them. They're also very smart and will greet you, get excited when they see they're about to be fed, and some seem to try and make you feel better when you're down! I have a friend (who isnt on here) who's betta will wake her up if he gets hungry when she's sleeping by ramming into his tank side hard enough to make a light clicking noise haha
I personally wish to see pics! we love to show off our babies here and see those other people own!