"Foriegn Experts Certificate" versus an "Alien Employment License"

Can you please help to tell me the difference between these two types of items? My friend just got her Work Permit WITHOUT leaving Beijing. Her original VISA was under her spouse's Z type. She first went to get a "Foriegn Experts Certificate" here in Beijing and then after that she went and applied and GOT her own Z type. She works at a school.

The KEY POINT here is that she did not have to leave China to get a Z type one before getting a Work Permit. Confused??

BR//Brian