My betta fish won't eat, help?

I got a betta fish yesterday and she'll take a bite of food and spit it out. I've tried tropical flakes, pellets, bread, goldfish food, and even a few bugs. She will bite it and spit it out. I thought she was sick so I took her out and put her in a small bowl. She wasn't so I put her back in my 10gallon aquarium and she would chase the guppies away and she bit my other females tail. Right now she's in a bowl. Im not sure what to do, HELP please. If you have any details needed ask me and i'll add it on additional info. (; thanks