What we know Bixbite Gemstones so far are that they are pinkish red in color. So, this one's gem could be pinkish red. Sure it looked green, but that's due to it being in a Nightmode Hue of Ronaldo's Camera. There are still speculations that her gem might still be red. Any others?
well bixbite's colors appear based on a rough untreated bixbite, explaining her yellowish orange color scheme, so chances are her gemstone is colored similarly (given its shape, it could honestly be the spike on top of her head)