She returned to SmackDown! on June 2, 2006, this time working as a villainous character with a "sexy teacher" gimmick, pulling on her real life experiences. Upon her arrival, she aligned with Kristal Marshall to feud with Jillian Hall and Ashley Massaro. This feud led to a Fatal Four-Way Bra and Panties match at The Great American Bash, which Massaro won. She won her first match on the July 28 edition of SmackDown!, defeating Hall by illegally using the ropes as leverage. Soon after, she began acting as valet for the team of K. C. James and Idol Stevens, who, because of her with them, were nicknamed The Teacher's Pets. The trio began feuding with Paul London and Brian Kendrick, and their valet Massaro, for the WWE Tag Team Championship, but never won the title. The feud ended when London and Kendrick won a match against them at No Mercy in October. On November 28, McCool was hospitalized with an enlarged kidney, a broken sternum, and an electrolyte imbalance. She was released from the hospital on December 2.
McCool returned on the March 30, 2007 edition of SmackDown!, where she participated in a 10-Diva tag team match. On the April 13 edition of SmackDown!, McCool became fan favorite once again when she came to the aid of Ashley Massaro after she was attacked by Jillian Hall backstage. On the May 28 edition of Raw, McCool won the Memorial Day Bikini Beach Splash Battle Royal by eliminating Melina. Subsequently, a series of matches took place between Victoria and McCool, including a Mixed Tag Team match where Victoria and Kenny Dykstra defeated McCool and Chuck Palumbo.McCool then became caught in the middle of a feud between the villainous Jamie Noble and her on-screen friend Chuck Palumbo. After a series of matches between the men, Noble won a date with McCool by defeating Palumbo in a match. In the storyline, Palumbo accidentally elbowed McCool during a match, causing her to suffer a concussion. The partnership was dissolved when McCool refused to accept his apology. She then went on to compete in a series of contests with Victoria, Eve Torres, Maryse and Cherry to determine SmackDown!'s top Diva, subsequently winning the title. At The Great American Bash on July 20, 2008, McCool defeated Natalya Neidhart to become the inaugural WWE Divas Champion.On the December 26, 2008 episode of SmackDown!, McCool lost the Divas championship to Maryse. After the match McCool turned heel by attacking Maria, the special guest referee of the match, and blaming her for the loss. In the following weeks, McCool also attacked Eve Torres, resulting in Eve's debut match, which McCool won. McCool then defeated Gail Kim on the May 22 taping of SmackDown to become the number one contender for the WWE Women's Championship. A month later at The Bash, McCool defeated Melina to win her first Women's Championship. As a result, she became the first woman to have won both the Divas and Women's Titles. During a rematch on July 26 at Night of Champions, McCool once again defeated Melina to retain the championship. Michelle had since formed an alliance with Layla, and entered into a feud with Mickie James, which resulted in a five-on-five Elimination match at Survivor Series. Mickie James then became #1 Contender for McCool's championship at TLC: Tables, Ladders & Chairs. Michelle retained her Women's Championship against James. That next night on Monday Night Raw her team lost a 7 on 7 tag match, although she was never tagged in.