Under current USCIS policy, an adjustment of status applicant with a valid EAD card can remain in the US and work irrespective of whether they hold/maintain a valid nonimmigrant visa. As a general rule, it is preferred that an AOS applcant continue to maintain valid nonimmigrant status, although it is not technically required.
You can file for your wife's change of status to H-4, if you wish, but she can remain in the U.S. lawfully as an "adjustee" as long as her I-485 application for AOS is pending with USCIS.
Disclaimer: The information provided here is generalized and should not be relied upon as legal advice. This communication does not create an attorney-client relationship.
Her status ends with her job. A change of status would need to be filed BEFORE her employment ends.
J Charles Ferrari Eng & Nishimura 213.622.2255 The statement above is general in nature and does not constitute legal advice, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship. Answers on Avvo can only be general ones, as specific answers would require knowledge of all the facts. As such, they may or may not apply to the question.