Okay, first off a one gallon tank is only barely enough for one fish.
Second, male and female bettas should not be kept together. The male is just flaring at her right now but soon enough he will try to kill her to keep her out of his territory. Males and females are only put together during breeding and that is done under intense supervision and in no less than a 10 gallon tank. The pair has to be conditioned for breeding and the female must be removed immediately after or the male will kill her defending his nest.
Remove the male immediately and get him his own tank of at least 2.5 gallons. The female will do better than he will in a one gallon tank. Make sure you do 100% water changes at least once per week to remove harmful ammonia.