My 3 yr old daughter just had the same thing. She is a nail biter and got a little too aggressive. What I did was soak her finger in very warm Epsom Salt water for a few minutes. Then I took a Q-tip with hydrogen peroxide and started gently pushing the skin away from the nail. I finally found the "wound" and gave the finger a quick squeeze. It hurt for a second until it opened and puss squirted out. I put more peroxide on it, then a band-aid with Neosporin. It was MUCH better the next day. My uncle-in-law said it needed to be opened and drained before the body could do it's job. If you can't handle causing your daughter a little pain, take her to the doctor.