What sort of a visa is sufficient to keep my wife here as she waits for F2-A priority date to become current?

If you use a non-immigrant visa with the deliberate intention of short-circuiting the system and eventually adjusting, you are misrepresenting your use of the visa. Sometimes they can prove this in expected ways, and then you are toast. Now you may be ok if the short-circuiting is a by-product of a real other motive - for example when it occurs two years into a four year degree. Or if your wife was working on an H1B.