How can my wife get a security clearance so that she can find a better job?

A security clearance is granted based on a job billet (position) requiring access. She'll have to apply for a job that requires a clearance not contingent on already having one or work in an organization that has a clearance position that one can move into. My two cents...

Apply away. BTW take a look at the job advertisements. If it says a clearance is required to apply, then don't. You should seldom see that unless the technical aspects are classified and you'd have to have a clearance and doing a lower level of that classified work to qualify. If it says a clearance is required to perform the duties, apply. Requiring a clearance up front makes the candidate pool much smaller. In the OPM circles, the process is to select the best and then get them a clearance. That's what "interim" is used for while you're waiting for the rest of the stuff to catch up.