These will both be helpful to your wife. American Dental Association (for accredited programs & exam info by state):
ADA.org: Dental Assisting, Hygiene and Lab Technology Programs - U.S. (http://www.ada.org/prof/ed/programs/search_dahlt_us.asp - broken link)
There are 3 schools in MS who offer the only accredited Dental Assisting programs in that state, which she can call prior to moving, to have her bases covered.
US Dept. of Labor, Bureau of Labor Stats. Best info Re: Assisting:
Dental assistants
Best of luck...