va2ba said:
This needs to be said again, do not under any circumstance let the state department know that you two are a couple. If they know this, there is zero chance of them letting her come to visit. And she needs to make sure that she has sufficient ties to Argentina to convince them that she won't stay and this is much easier said than done. Owning property is the best way to convince them that she will come back.
The following is only my personal experience so it is in no way definitive, but I have to refute the "zero chance" statement made above. I'm a US citizen and my fiance is a naturalized Argentine. We decided to try to have him come to the US to visit my family in December for the holidays. Originally we planned that he would say that he wanted to visit friends and wouldn't mention my name or my family. After talking to an immigration attorney in the US we decided to tell the truth at the embassy and take our chances. The attorney made the very good point that it is never a good idea to lie or hide the truth from the state department. He told me that my fiance had less than a 50/50 chance (in his opinion) of getting the visa since we're both young (early 20s), he's an immigrant to Argentina, doesn't own any property, etc. We gathered all the relevant documentation (lease, documents showing he's employed and in school, even his parent's relevant documentation) and I asked my mother to send a letter of invitation.
On the day of his appointment I went to the embassy as well. The woman interviewing us was very nice and as soon as she realized that I'm American and speak English she stopped speaking Spanish and instead directed her questions to me to translate. We offered to show her all the papers we brought but the only thing she wanted to see was the letter from my mom and documentation from my fiance's university. After about 10 minutes of pretty basic questions she gave him the tourist visa for 10 years, wished us safe travels and good luck on our engagement and sent us on our way. She did warn us that he should NEVER overstay his tourist visa, especially since we're planning on moving back to the US in the future, but when I explained that I'm also working here (and that I'm dealing with Argentine immigration myself) she relaxed.
We went to the US in December, had no problems with customs/border control and had a lovely time. I realize that this may not be relevant to the OP's situation, but when I saw that people were writing in such absolutes I decided to share. I expected a much more difficult experience (mean interviewers, lots of personal questions, etc) and instead found it quick, painless and even pleasant.
Again, I don't know if we were just lucky or what, but in my opinion it is better to tell the truth than take the chance that the state department finds out the truth. If any sort of fraud is detected they can revoke your visa permanently. Our experience shows that it is possible, even without property or very strong ties to Argentina, to bring a significant other to the US on a tourist visa without lying.