You may want to consult with your local US embassy or consulate for the official answer to this question. From my layperson's understanding, a B1/B2 is usually tied to some form of business relationship. How likely she would be able to move to the US for 1 yr+ depends in part on how strong her ties are to the US and to her home country, as well as the (perceived) "intent" behind the visa application. Generally, B1/B2 visas are eligible for up to six months, with an extension of six months sometimes granted.
To be honest, these days it seems to be harder to get someone who is not a spouse, child, or officially recognized partner to obtain a visa under the conditions you have sketched, above. If you were to get married, you would have the option of an F-2 visa, I believe, as you would be receiving an F-1 visa.
Other visas you could consider exploring (but that have varied requirements) are H1B and J-1. Both (I believe) require an element of sponsorship, though.
Victor M. Lee
Class of 2011