Sisters surprise stepmom with adoption papers for her birthday: 'My heart is very full'

"I seriously wouldn't be the woman I am today without her," one daughter said.

— -- Two sisters from Pennsylvania gave their stepmom an emotional birthday surprise: asking her to legally adopt them.

"I had no idea they were doing it. It was the best birthday ever," Diana Gopear of Lewisberry told ABC News. "I always felt like they were my own. There was no difference. My heart is very full."

In 1998 she met Dennis Gopear, and three years later, they married. He had two daughters from a previous marriage, and Diana Gopear said she loved them from the start.

On March 30, her 46th birthday, her stepdaughter Emily Gopear, 20, gave her a gift: a stack of papers. Written on them were reasons Emily Gopear loved her so much. At the bottom of the stack were adoption papers for Diana Gopear to sign. The moment was captured on video.

"She is like no other woman I know," Emily Gopear told ABC News. "She came into our lives when we were young. She could've left at any time, but she didn't. She stayed. She's my best friend. I seriously wouldn't be the woman I am today without her."

The next day, Emily Gopear's sister, Christina Gopear, 23, asked Diana Gopear to adopt her too.

"I had this whole speech, and she was crying," Christina Gopear told ABC News. "At the end, I got down on one knee and said, 'Will you adopt me?' She hugged me, and it was one of the best feelings."

Emily and Christina Gopear's birth mother divorced their father when the girls were a toddler and 5, respectively. She has not been a part of their lives since then, the women said.

During the holiday season, the sisters spoke to Diana Gopear about moving forward with the adoption process, and in March they made it official.

"Now that I'm an adult, I've come to the conclusion that she deserves to be recognized for everything she's done for us," Christina Gopear said. "She put her life on hold sometimes for Emily and I. She's always considered us as her own."

"I love how caring she is and how she's always there for me," she added. "I was a rough child to raise, growing up, and she's always stuck there by my side. No matter how bad things got, she was there."

Diana Gopear signed the adoption papers, which will be finalized over the next two months, for both women.

The Gopears plan to have a nice dinner to celebrate the special event, Emily Gopear said.