bettasareawesome: I raised my baby betta (the first one) for a few weeks in the breeder net inside my ten gallon. I fed her through a medicine syringe (so that no food went to the bottom and so I could make sure she was eating everything I needed her to eat), so every time she sees it now, she knows to come up for it..she just eats straight out of the medicine syringe..like I don't even pump it out for her. (If that makes any sense). She now jumps for it, which is convenient for me because my fat molly can't jump
so i just hold it an inch above the water to feed her
You could try the syringe and get her used to it..or, like chocolate betta said, separate her during feeding time..if you still have the cup that you bought her in, you can cup her, feed her, and then release her back into the tank..or if you don't still have the cup, I'm sure any tupperware or something would be fine
I think that feeding through the syringe is helpful because you are not just dispersing all the food throughout the water...you are keeping it confined to one area that you want only your betta to get to and the others can't steal it because you have full control over it
Let me know if this helped at all!