你好.你的句子没有问题.是你们老师的英语思维太死板.因为你指的是过去的事情,所以必须是stayed或者是was.你是对的.又如：
When he stayed with us here in Shanghai(==While he was staying with us in Shanghai),he visited three senior high schools.当然,你的句子也可以改写成：While I was staying in China,I always spent my time with Lucy. 反正,你的句子没有错. 又如：When he was in Shanghai in 2009,he stayed with me for three months ====== When he stayed in Shanghai in 2009, he was with me for three months.