Your question was submitted to the offices of the maraje’ and these are the responses that were received:

The office of the Grand Ayatullah Khamenei:

In this specific case, she shouldn’t refuse to comply unless there is a considerable harm in it for her.

The office of the Grand Ayatullah Sistani:

It is permissible for her to refuse to comply in the case of the disease being transmitted to her, even if its transmission isn't for sure and there are only chances of such. But if there is a way to lessen the chances dramatically say to a two percent chance of its transmission (by using protection for instance), then it is permissible for her to comply and actually as an obligatory precaution, it is necessary for her to do so.

The office of the Grand Ayatullah Makarem Shirazi:

You need to take him to an expert doctor and in the case of the doctor confirming the disease, you can refuse to comply.

The office of Ayatullah Hadavi Tehrani:

If the disease is dangerous and can be transmitted through intercourse, not only will compliance not be obligatory, but will also be impermissible.

For further information, see:

1- Lustful pleasure and its boundaries, Question 551 (website: 601).

2- The boundaries of lustful pleasures in wedlock, Question 2105 (website: 2177).

3- The duties of wives regarding their husbands, Question 850 (website: 925).

4- Compliance of wives with their husbands, Question 1674 (website: 2310).

5- How much wives must comply with their husbands, Question 5846 (website: 6064).

6- The Muslims’ responsibility towards fighting aids, Question 4045 (website: 4411).