用does she
跟I think 这种不一样,如果是I think Tom sings best in the class,就用doesn't he?
如果陈述句为含有宾语从句的主从复合句,反义疑问句的谓语动词和主语代词一般同主句的谓语动词和主语保持一致.但是,如果陈述句为“I (don't) think,believe,suppose,figure,assume,imagine,expect,feel等+宾语从句”,反义疑问句的谓语动词和主语应该同宾语从句的谓语动词和主语保持一致,如果主句是否定式,反义疑问句要用肯定,反之亦然.请比较如下例句：
I think you will come to the meeting,won't you?(反义疑问句的主语和谓语同宾语从句的主语和谓语一致,因为主句是“第一人称单数I+(don't)think等动词”)
Mary thinks you will come to the meeting,doesn't she?（主句的主语不是第一人称时,反义疑问句的主语和谓语要同主句的主语和谓语一致）
祝英语学习成功.