Preston was expected to appear at the California Governor's Conference for Women in Long Beach, Calif., in October, which Maria Shriver hosts, but she has withdrawn from the speaking engagement.
"It is with my sincere apologies that I must pull out from speaking at [the] conference. I am sorry, but I truly believed that I could do it," Preston said in a statement to People. "Otherwise I never would have said that I could. But I am still deeply in the process of healing, and it's just too soon."
Preston was due to speak on the "Grief & Resilience" panel.
Shriver, the wife of California Governor Arnold Schwarzenegger, just loss her own mother – Eunice Kennedy Shriver, who died earlier this month at the age of 88 — and earlier this week, her uncle, Ted Kennedy, also passed away at 77.
Knowing loss all too well, Shriver said she was supportive of Preston's decision to pull out of the conference.
"I know how hard it was for Kelly to make this decision and she has my complete support and understanding. Everyone has their own path to healing and their own timetable for grieving," Shriver said in a statement, People reported. "Kelly's presence at The Women's Conference will be missed, but the main stage conversation on grief and resilience with Elizabeth Edwards, Susan Saint James and myself will continue as planned. Having just lost my own mother and my uncle, I believe it's an important and meaningful subject because loss and grief will touch everyone at some point in their lives."
As previously reported on AccessHollywood.com, Kate Gosselin of "Jon & Kate Plus 8" will appear at the October conference.