"This is it guys. It's time. Love you all n tweet to ya again when I can. Xoxoxo," she tweeted before the birth.
Alijah is a form of the name Elijah, which means "the Lord is my God." Mary could be in reference to Hefner's late secretary, Mary O'Connor, who died last year at age 84.
Wilkinson was especially close to O'Connor and wrote in a blog post after her death that she was "almost like a therapist" to the people in Hefner's Playboy Mansion.
"When I lived at the mansion I was very close with her. Over the years, she helped me through a lot and was always there for me," Wilkinson wrote at the time.
Wilkinson and Baskett also have a 4-year-old son, Hank Baskett IV.
Notable deaths of 2014 [PHOTOS]