MacKenzie said in the first book that she is going to enroll at Westchester Fashion Institute of Cosmetology, which is owned by Clarissa.
In the second book, Clarissa makes an appearance. After Brianna's ballet recital, she asks Nikki to face-paint little girls at a ballet party held at Westchester Petting Zoo. It can also be assumed that she has a daughter, since Nikki called her a "Ballet Mom".
She was briefly mentioned in the fourth book and it is unknown if she will appear again.