She thinks that he's on a diet, ______?
Can anyone tell me which question tag best fills in the above blank? Should it be "doesn't she?", or "isn't he?"
I'd like to stick to the usual affirmative-negative form (or vice-versa) of tag for my middle school students, who just began to learn the basic rules of this grammar. Therefore, should the tag refer to the main (hence, doesn't she?) or subordinate clause (isn't he?).
I have a feeling that, in terms of question tags, the case of You/She/He thinks should differ from that of I think, because it doesn't seem to make sense to ask others if you think in a certain way. Am I also right about this?