How far in advance should she schedule the appointment?

You can get the results the same day or the next day so make the medical appointment a few days prior to the interview.

Not too far, some clinics like MOM won't let you schedule an appointment if it is going to be more than a few weeks out.

Olga tried the Vladivostok Clinic and was told 12 days. When she was actually going to have it done the doctor was leaving for Moscow

She had it done during her 3 day stay in Moscow but we were both worried it would not be done in time!

Galina scheduled her medical 4 weeks before her interview. But she was told she couldn't get the results until the following day. She went to Moscow one day early so she could get her results.

You can schedule it once you find out the interview date with the actual appointment as close to the interview as possible. Most folks have scheduled it the day before or two days before the interview to cut down on the time spent in Moscow. (To save money on lodging in the big city.)

If she's closer to Vladivostok, that is also a good option. The check is good for a little while (I don't remember how long, at least a few weeks) so she can do it there or in Moscow. But, like Marc said, scheduling there could be a problem as well.

Your best bet is once you find out the interview date, have her call the medical office and set an appointment for the day before or two days before her interview date.