Hi I'm new to owning a betta. I've wanted one for a long time, and my mom bought one for me for Christmas. It is a Half Moon Betta, I'm not sure if it is male or female. At the moment I have a 1 gallon tank, at some point I will upgrade. I have an under gravel heater because my house is always cold, and it was recommended by one of our local pet stores. I have read numerous places that they can picky eaters, which the local pet store doesn't seem to know.
My fish will go to eat her pellets and then spit them right back out at me... It seems hungry but it refuses to eat the food. I am wondering are flakes better? We called the pet store and they told me that she was probably sick.

Its fins are fine (no rot from what I can tell) and its swimming around all the time. Any advice would be greatly appreciated