The "Just Like Fire" singer took to Instagram on Sunday to share a snapshot of Willow changing a diaper on a baby doll, which Pink captioned, "Dry Runs."
In 2013, Pink opened up to Billboard magazine about wanting to give Willow a sibling, sharing, "My brother is everything to me. So I want her to have family beyond her papa and me."
"I mostly want another one for her to have a lifelong friend," she added.
Willow also played a very special role in the 37-year-old singer's heartwarming pregnancy announcement, which she shared two weeks ago.
In the pic, Pink and Willow stood in a tree-lined field, basking in the warm light of the setting sun as the singer's daughter rested her head on her mom's already sizeable baby bump. Check out the video below to see the beautiful announcement.