WE are overwhelmed. Following our appeal yesterday for help in getting three-year old Yau Tsz-ying to Japan for urgent medical treatment, the response has been tremendous. Cathay Pacific called us to say that they would fly Tsz-ying, her parents and, if necessary, her doctor to Nagoya for the life-saving operation through the airline's Charitable Travel Fund. A prominent businessman, who asked to remain anonymous, sent us a cheque for the $116,000 needed to cover the medical bills. All day yesterday, Keeping Posted also kept receiving other offers of cash donations - both large and small - and many messages of concern for Tsz-ying. To everyone, we say a big thank you. The extra cash will be used by the family for other expenses connected with the trip which will be quite substantial. Tsz-ying's mother Yau Lau Mo-kit was almost overcome with joy when she heard the news. ''I want to thank all the generous readers so much,'' she said, before rushing off to fax X-rays to Nagoya.