Outlaw,
Your wife can get her cdl class b by going to the dmv in TN and taking the written test to get her temp. Once she passes the written test, then she can take the road test by either renting a vehicle that has air brakes and rated over 26,000 gvw. You can usually find one of these at a local rental place or sometimes the state can provide you with a testing vehicle at a fairly reasonable rate. Once she gets her hard copy cdl, then you have to decide if you are going owner op right away or look for a fleet ower that has openings and will hire someone with a fresh cdl. Some companies do require both drivers to have 6 mos experience or more, however quite a few will allow the 2nd seat to operate as long as they are with an experienced partner.
Good Luck,
ABC