Hi,
My spouse came to US in Feb 2005 on H4 visa. Then she applied for H1B in Oct 2007 which was approved but never worked with the employer. In Mar 09 I renewed my H1B and also her H4 visa as I was not sure what her status was. Fortunately both H1 for me and H4 for her were approved in Mar 09. Now she wants to being working as she completed her masters. Question is can she work under her existing H1B with the old employer which the old employer never revoked or she needs to apply for new H1B to work? Also if you could explain the reason of your advice.

Thank you.