She told God that she would not date anyone - man or woman - for an entire year, so that she could focus on her relationship with him. That day, she attended a prayer meeting with a friend, which left her feeling overwhelmingly at peace, "indescribably happy," with a "hunger for God" and everything that he wanted for her life.
Zember's life changed drastically that day. She turned fervently to her mission work, she sent messages apologizing to all the people she had hurt throughout her life. Her taste in music and movies changed, and she felt a true sense of freedom.
That day was real, Zember wrote, and the year of no dating and pursuing only God was one of the most spiritually fruitful in her life so far.
But that doesn't mean she was perfect from that day forward, she noted. In the following chapters of the book, Zember recalled how some well-intentioned relationships turned sour, and how she continually needed - and still needs - to keep turning back to the Lord.
"I speak on a lot of Protestant platforms and, I get asked the question all the time - 'When were you saved?'" Zember said.
She said she likes to respond: "'Well, let's be real. It was at the cold waters of baptism when I was an infant.' That always strikes up a conversation."
Zember said she included these moments of stumbling in her book even after her surrender to God because conversion is not a "one and done" process.
"There's a cooperation of grace. His grace, I cannot earn. His grace, I do not deserve, but I can receive it and I can ask him to help me to work with it," she said.
"Through this process of many different encounters I've had with the Lord daily, I believe he's sanctifying me just as he is everybody else from day to day. It's not a one hit. He's not a magician. It's a relationship. My relationship with him is constantly growing, especially the more I seek him."
Zember never intended to publicly share her testimony about her relationship with God and her same-sex attractions.
"I actually resisted it," she said.
While accompanying a friend doing ministry at a women's prison, Zember felt God calling her to speak about homosexuality, and she told him: "That ain't me, God. I suggest you whisper that to someone else."
But the calling did not go away, and Zember finally gave in - and volunteered to share her testimony at the women's prison.
"I realized what was holding me back was myself, and what will people think of me? What about my reputation, or my image, or self-love?" she said.
"And so, I thought, 'Okay, well, you know what? It can't hurt. Well, it could hurt actually,'" she said, noting that she was afraid she might get "beat up" for speaking about such a controversial topic at a prison.
"But I thought, I'll try it this one time, because apparently there's a big need, and we'll see what happens."
To her surprise, nobody left the room during her testimony. Many were crying, and by the end the women stood up and applauded. Many wanted to talk one-on-one afterwards.
After that talk, Zember shared her testimony more freely, and soon enough she founded her second ministry, Overcome, for people who also want to live in Christ's truth about homosexuality.
The ministry started as more of a landing page for all of the "overwhelming" responses she was getting to sharing her testimony, Zember said.
"But all positive. All people seeking hope," she said. "And sharing that they found hope in what I shared, and that they desire the same thing or similar in their life...it was a flood of people reaching out from all over the world."
Like with her other ministry in Ethiopia, Zember said she started Overcome ultimately because of an invitation from God.
"So again, God invited me to say, 'Hey, can you stop looking at yourself and see the need that I have before you?' He doesn't need me, but he does say that the harvest is ripe and the laborers are few. And so I was like, 'Okay, well then, let's do this.'"
It was out of this same kind of invitation that Zember wrote her testimony in "Restless Heart." And her message, she said, is a simple one.
"I pray that people can see that God is good, that he loves us, and that he is for us and not against us. And every one of his ways, that have been preserved in Scripture, that have been preserved by the Catholic Church, are for our good and for the glory of God."