"She's going to be fine," Wilson, 41, tells The Insider. "Anyone that goes into rehab needs help. She knows how much I love her. She's my lifelong friend and my oldest friend. I wish her all the best in her recovery."
Asked if they will perform together anytime soon, Wilson says, "We will."
Chynna Phillips, who turned 42 on Friday, is the half-sister of Mackenzie Phillips, who said last fall that she had once had a sexual relationship with their father.
Chynna was shaken by those claims, but a source said her decision to seek treatment was based on "a combination of things."