Full color generally takes like twice as long as black/grey for any given size. If its more hard lined, neo-traditional, you could always do the outline and the black shading in a session, give it a month or two to heal, then go back and do the color. If you want it more like a water-color/oil painting style, then maybe they just gotta go thru. Color is hard on skin because you're essentially going back over the same spot like 3 or 4 times... line, black shading, colors and fades between them. So its a lot of trauma on a small region. Just gonna have to take your time. Also here's the chick: That whole area is 10x more painful than a forearm. If she can do it, you can do it.