The How To Get Away with Murder star's sibling was assaulted by a man when she was just eight.
"Myself, my mother, my sisters, my friend Rebecca, my friend from childhood, we all have one thing in common: We are all survivors of sexual assault in some way, shape or form," she said at the organisation's annual fundraising brunch in Beverly Hills, California on Sunday (25Sep16).
Organisers at the foundation provide free medical treatment, counselling and legal aid to sexual assault victims at their Rape Treatment Center and Stuart House and Viola wants people to visit the facilities and become supporters.
"You must," she said. "And then let your heart do the rest."
The 51-year-old has been an advocate for the foundation since 2010 and last year (15), she opened up about her sister's assault, revealing she has been trying to help her sibling, who has struggled with substance abuse and homelessness, but has been unable to.
"A precocious, very intelligent, very creative child grew up to be frail, angry, a drug addict by the time she was 20," she said at a benefit for the Stuart House charity in November (15)... "You pray that she finds peace and love and happiness, she gets off drugs. And then of course you open your eyes, and you're like, 'She's still on the streets...'
"I wish I could tell my sister that she's not dirty, and that she should not feel any shame for something that she literally was not responsible for. I wish I could save her life."
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