Females will flare at males. The thing is - how is she flaring? If she is constantly trying to break through head on, she is in fighting mode. But if she is swimming all over her tank and returns to flare, she is most probably in breeding mode (males must do this as well).
Give her time as you condition her further. Flare her to a mirror (since you don't have another female). place the mirror at the bottom part of the tank or cover the top part of the mirror. Give her only an inch of sight. Let her flare for 30 min or so. Then rest her in total isolation until the following day and try re-introducing them. See how they act/swim.