When Millie Smith was 30 weeks pregnant, she gave birth to identical twin daughters Skye and Callie. Callie was rushed to intensive care, while Skye — who was born with a incurable brain condition called anencephaly — survived only three hours. But the new mom and her husband, Lewis Cann, packed a lifetime of love into those three hours.

“Lewis and I cuddled with Skye … and talked to her about our family and how we wished she could have grown up with her sister,” Smith tells Us Weekly. “We told her how much we loved her. And I told her I was sorry that I hadn’t created her properly. I felt like it was my fault. I knew it wasn’t, but I always felt guilty. We told her she would never be forgotten.”

Days later, when the grieving mom was visiting Callie in the Neonatal Intensive Care Unit at Kingston Hospital in the U.K., an exhausted parent of twins turned to Smith and made an innocent comment that broke her. “She said, ‘You are so lucky you don’t have twins,’” Smith, 24, tells Us. “Up until this point I hadn’t cried in front of any of the parents. But that was it, I ran out of the room in tears.”

Smith continues: “I didn’t have the guts to go back in and tell our story. I didn’t want her to feel bad. The comment wasn’t meant to be spiteful and was probably more out of jest, but it was heartbreaking.”

That is when the Surrey, England–based estate agent came up with the idea to make purple butterfly stickers for NICUs to help identify when a baby has survived the death of one or more multiple-birth siblings. The stickers, which are now at Kingston Hospital, read: “When visiting this Neonatal unit as either a partner, relative or friend please be aware of the butterfly logo on each cot. This represents a baby that was part of a multiple pregnancy but sadly all of the babies did not survive.”

“I chose butterflies because as I felt it was fitting to remember the babies that flew away,” says Smith, “purple because it is suitable for both boys or girls.”

She has been blown away by the response. “So far about 115 hospitals have contacted me wanting to implement the idea,” Smith tells Us. “I thought it would just be our local hospital!”

Smith started a crowdfunding page called Skye’s Wish to support the butterfly stickers and help create support groups for families who lose babies during pregnancy or birth.