A devout Christian, Mary Lou Wallner grew up believing homosexuality was a sin. So she was devastated when, in 1988, her older daughter Anna, 21, told her she was a lesbian. Wallner's reaction—and Anna's subsequent suicide—haunt her to this day. Now, as head of TEACH Ministries (www.teach-ministries.org), which Wallner founded in 2001, she and husband Bob speak to Christian groups around the country, urging parents to accept their gay children. At her home in Little Rock, Wallner, 62, whose story is featured in the documentary For the Bible Tells Me So (www.forthebibletellsmeso.org), spoke with PEOPLE's Bethany Lye.

I was so excited to get a letter from my daughter at college! But after reading what Anna wrote—"I love women"—I went to the bathroom and threw up. I wrote Anna a terrible letter. "I will never accept that in you," it said. "I will continue to love you, but I will always hate that."

Like any mother, I dreamed of Anna marrying and having a family. She was smart; at 10 months she could hum "Jesus Loves Me." As a kindergartner in Christian school, she quoted 100 Bible verses from memory. When she was older, she was a ventriloquist and loved music and drama. Looking back, there were signs. Once, in high school, with her friend over, she said, "Kelly's mom thinks we're lesbians." I should have seen it, but I didn't.

After Anna's letter, I prayed she would change. I felt she was committing a horrible sin and needed to ask forgiveness. We shared it at church: "Would you pray for our daughter?" And of course everyone thought it was wrong too. Anna and I even saw a counselor; she was kind, but her nonverbal language was, "There's nothing wrong with this." I couldn't make that part of me.

The next time I saw Anna, at my ex-husband's home for my younger daughter's graduation, she had a partner with her. I had to go into another room and cry—I couldn't stand seeing them together. She brought partners home; we were cordial but didn't want them sleeping in the same bed.

In 1996 Anna began pulling away. I'd try to contact her but wouldn't hear back. Months later she sent an angry letter. She said she didn't want anything to do with me, that I had done colossal damage to her soul with my shaming words. Some of her letter's last words were, "Heal thyself, Mother."

After six months of silence, the phone rang. It was Feb. 28, 1997. Bob answered, then sat down, looking like someone had knocked the wind out of him. "It's Anna, isn't it?" I asked. She had hanged herself from a bar in her closet; there was no suicide note. I later learned that Anna [a social worker] had gone on disability for depression.

That year Bob and I began reading books on homosexuality and really studying the Bible. It was a big jump for us, almost a yearlong process. In the end I found myself far away from the safe place I'd been all my life. I wound up on my knees praying, "God, are you sure you want me to change my mind?" And I had an epiphany: This is not a sin. These people are just like we are; they want the same things we do.

Suddenly I could not keep silent. I went to rallies and conferences, telling Anna's story and mine. In 2001 I gave our story a name: TEACH Ministries. It stands for "To Educate About the Consequences of Homophobia." There used to be no other option than to believe what we were taught. But now I know the value—the power—of unconditional love. And though it came too late for Anna, I believe she knows what we're doing. And she is proud.