I've looked in Murphy, Swan, Alexander, and Huddleston & Pullum. I can't find anything that indicates that the following sentence is wrong, but somehow it doesn't sound quite right to me. Yet I think I saw something, in passing, when I was looking for something else.

Or perhaps I'm just unsure because, being American, I don't use must very often. Is this tag OK? (I can't change the anchor.)

She must wear a suit to work, mustn't she?

Thanks.

Yes, my friend, that tag question is fine. I understand what you mean about a phrase like this not being commonly used by speakers of AmE, but it's correct.

The sentence sounds awkward to me, too, Okaasan, but it is grammatically correct, as Richard states.

It would be a service to your students to tell them just what you have expressed here -- that 'must' in a tag ending -- even 'must' itself for obligation -- is not used so much in AmE.

If the meaning of that sentence is expressed, it would be more natural to put it this way:

She has to wear a suit to work, doesn't she?

If you must use 'must,' how about this:

She must wear a suit to work, right?

In court or in very formal English, you might hear:

She must wear a suit to work, must she not?

Thanks, Richard and Rachel. Our textbooks use British English, which is not always easy for me. This bit about the modals of obligation are particularly hard for me because of the usage differences.

Our textbook doesn't teach "free" tags such as right? and isn't that so? so I can only teach the usual ones that repeat the auxiliary verb, etc.

Can you teach your students what's in addition to the material in the text?

In theory, yes. However, students here are so stressed to do well on the exam that I'd hate to give them extra. And I'd be afraid that if they did use something outside the usual, the person correcting the exam might not recognize it as a correct answer.

My daughter lost out on majoring in what she wanted in university just because she was 1/2 mark too low in English! So every little bit counts here.