The former EastEnders star, 49, has been open about her former cocaine abuse, which left her suffering damage to her nasal septum.
Opening up on Instagram, she said both her son and her daughter Jodie had been "trolled and bullied" as a result.
Sharing a snap of Kai – who at 26 is the oldest of her two children – she wrote: "I know in my heart he was sent to me for a reason.
"Being his mum has saved my life, blessed me and broken my heart. It broke my heart for all the pain, worry and embarrassment my selfish actions in addiction caused him.
"To this day and probably for ever more both Kai and Jodie will get trolled and bullied because I was a cocaine addict."
She went on: "This boy who’s now a man has always been the most loyal, loving and brutally honest person in my life. His (sic) shown me love and sometimes such tough love that no other in my life has cared that much to do.
"Everyday I wake up I thank God for my kids and their love. And I can say without hesitation if I didn’t have Kai I probably wouldn’t of made it."
The actor, who found fame as Sam Mitchell on the BBC soap, said God "blesses us when he makes us parents".
"Today I count those blessings and don’t intend to let anything or anyone take me off the path to rebuilding trust bonds and bridges that my addiction broke," Westbrook said.
"That’s why I’m constantly aware of my triggers and temptations today and I will never take for granted again just how cunning and devious my illness is. The day I think I’m cured is the day I am in danger."
She added: "And my dangerous Danniella days are behind me."
Westbrook has previously said using cocaine "ruined" her life and she has spent time in rehab in the past.