Too long of a question for a free consultation over the Internet.
Kindly be advised that the answer above is only general in nature cannot be construed as legal advice, given that not enough facts are known. It is your responsibility to retain a lawyer to analyze the facts specific to your particular situation in order to give you specific advice. Specific answers will require cognizance of all pertinent facts about your case. Any answers offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship.
Please consult with an immigration attorney. Your uncle's wife would have to reside in the U.S. after getting the green card.
Disclaimer: This answer is for informational purposes and does not take the place of a consultation with an experienced immigration attorney. This answer does not create an attorney-client relationship.
If you're confused about what forms and the types of photos you need, you will certainly be confused once you have to deal with the Consulate. Avvo is not an adequate substitute for legal representation based on the individual facts of your case. I would strongly recommend that you hire an attorney if you wish to avoid costly mistakes, which can result in the loss of time and money and the delay or denial of the case.
Answers provided by Ksenia Maiorova, Esq. on Avvo.com are of a general nature and do not constitute legal advice.
If all she wants is to "visit" the USA for 2 months, then I don't think getting an "immigrant visa" in order to enter the USA and gain permanent resident status at the time of entry is the way to go. For starters, she would not have "immigrant intent" so even "if" the Uncle went through all of that long and tedious process (including the payment of the NVC fees and the tedious pre-clearance of his I-864 affidavit of support) my worry would be that during the immigrant visa interview, the Consul would discover she only wants to make a short visit and would therefore deny the immigrant visa. Of course, I don't have experience with that scenario (trying to get an immigrant visa to allow a 2 month visit) as I would "never" approach this problem with that solution, so this is just my best guess (my worry that the Consulate would deny the immigrant visa because she actually has "non-immigrant" intent).
If it were my client, instead I'd try to figure out the best way to prove her "non-immigrant" intent (that she has strong ties to the home country that will compel her return after the brief visit) and try again to obtain the visitor visa.
Best of luck.
Matthew Udall - Attorney