Have you seen her coughing up blood or acting weak? Symptoms don't just turn off whenever other people are around. It doesn't sound like she has leukemia, but another disorder. CLS, compulsive liar disorder. Symptoms of CLS are major covering up (such as saying that no one had proof except her and her doctor), unusual actions (such as participating in gym class when she allegedly has an immune attacking cancer). I had a friend in elementary school who got leukemia. She was sick from school often, and didn't know why. When they found out, she was able to get treatment, and now she's perfectly healthy. It's not adding up. If she's 16, she should be going to the doctor with her parents. It's illegal not to because she's a minor. I say just ignore it unless she tries to use you with her "illness," then talk to someone and tell them what's going on. It's just petty kids-trying-to-find-themselves stuff until she tries to manilpulate you or someone else.