If she enters the US on a tourist visa, marrys you, and then attempt to adjust status (i.e., obtain an immigrant visa, aka green card), the INS will presume that she lied regarding her intent to stay in the US when she applied for her tourist visa. The INS very much frowns on people who lie to it.
My wife and I are a slightly different case as we got married in the US and then turned around and came back to HK. She was using a tourist visa. We talked to an immigration lawyer about 18 months ago about how and when we should begin paperwork for my wife to obtain her greencard. What a fucking headache. Thank god the lawyer is a friend of the family and we were getting free advice.
For our situation, there are two methods. The first is the consular route. We would have to first file paperwork to “verify” our marital status; this would be filed with the bozos at the US Consulate in HK. After they interview us and agree that yes, we actually are married, we can then apply for her greencard. At present, it seems that the average time to process everything through the HK consulate is two years. Some applications take longer; I’ve heard of none that take less than a year and a half. During this time, my wife is not allowed under any circumstances to enter the US on another type of visa since she is in process for a resident visa. I asked if my wife would be allowed to enter if one of my parents died; the lawyer said that would be extremely risky and that there are no allowances made for that type of situation. Our lawyer friend stressed that we should consult a lawyer before submitting any scrap of paper or attending any interview during the consular route process. She wasn’t just saying this to get business; she had already said she would do it for free.
The other route is to break the law. The attorney stressed that she was not advising us to do this (read: this is against the law, so I can’t directly recommend it, but it is the quickest way). My wife would enter on her tourist visa and then apply to change it after arriving. 18 months ago, this lawyer said that it would take about three months to get a green card through this route. HOWEVER, it is not 100% safe. She said that she had never had a client who was deported because of this, but that there is still some risk. We would also have to pay a fine of about US$700. Because of special circumstances, we would probably have to do it this way. We won’t do it, though, without first talking to a lawyer again.