It looks as if the nail has had some trauma which has caused the bruise. It will eventually grow out, but it may also fall off. I looks as if blood is under the nail plate. You definitely should refer this person to a physician if it bothers her. He may be able to drain the blood by piercing the nail bed. If its not problematic then leave it go. It's not a very aesthetic looking nail, but you can just polish over it, or use some glitter to cover it.