well, are u considering to buy the betta fish? i think it's pretty nice that they are keeping bettas in tanks, but walmart isnt a great place to buy quality fish if ur planning to buy it
sounds like she's pregnant. if she really is, consider separating the female so she can lay her eggs. once the eggs have been laid, take the female back to the original tank and keep the eggs at a fairly warm temperature + heater and a light filter of some sort.