If she wants to get a green card through her employer, she first has to get an H-1B visa. They cannot sponsor her for a green card without this intermediate step. The company would need to show that she has special skills and they cannot find anyone in the US who has the qualifications for the job and wants the job.
Even if they were willing to sponsor her for an H-1B, and they successfully jump through all the hoops, I believe she still has to go abroad to get her visa. If she has overstayed her welcome here by a year or more (which it sounds like she has), she will trigger a 10-year bar to re-entry when she leaves the US to get her visa.
Her only method of obtaining residency, as far as I can see, is if she were married to a US citizen.