A letter of invitation will in no way affect the speediness of the visa processing. The only thing it does is show that the person will have a place to stay while in the U.S. and therefore not need as much cash on hand when he enters. It may or may not help a bit. Often, visa officers at the embassy interview pay no attention to these letters at all. The BIG issue visa officers are interested in at the interview is if the applicant can show compelling evidence that he will return to his home when he is supposed to...and not overstay his visa. He needs to have a home, business, job waiting for him, money in the bank...things that will compel him to return. She needs to use the 2nd site below to begin her application for a B-2 tourist visa and follow all directions there. When he gets to the spot where he needs to make his visa appointment, it will tell him how long the wait time is. See last 2 sites for info and sample invitaion letters. Remember, unless the person is coming to the u.S. for a family event like a wedding on a certain date, or to attend a conference or class on a certain date...getting the visa appointment dated expedited is not going to happen.
As Charlie has already told you a letter of invitation would not speed up the application process. Tourist visa are processed on first applied - first served basis. The only way to speed up the process is to apply for the visa at a consulate with lower waiting time for a visa interview. The present waiting times (in calendar days) for a B1/B2 visa are:? Moscow - 20 days? St. Petersburg - 7 days? Vladivostok - 2 days? Yekaterinburg - 2 dayshttp://travel.state.gov/visa/temp/wait/t�� ..