In my opinion, you sister might have the OCD. This is a condition where repetitive behavior is used to reduce fear, apprehension or anxiety. You can also consult a doctor to make the proper and right diagnosis. You can also be advised on the best course of action to take. See details at http://en.wikipedia.org/wiki/Obsessive%E2%80%93compulsive_disorder.
OCD doesn't get better on its own and it's much easier to address now rather than later after it gets worse. There's no reason to wait anyway because the treatment isn't complicated or overly expensive. No one should feel compelled to do repetitive tasks like handwashing (or cleaning or counting etc,,,) all day every day. That isn't living.
10 months ago
Last edited at 8:50AM on 7/1/2012
Heynineteen is right, Sheng. Something has worried your sister about infection, and she has got stuck in a routine. Being clean is good, but not so often - a competent doctor will be able to advise, and the treatment is relatively easy.