The artist Carrie Mae Weems recalls sitting at her desk in Syracuse in 2014 “feeling very anonymous and misunderstood and trying to figure out how to make some new work” when she got the call.

“I was offered this extraordinary gift,” she said. “It was important, because I needed the money, but more than anything, I needed the encouragement and the support to keep making, to keep pushing — to continue to work in spite of all of the pressures.”

The gift is part of a grant program that has paid out a total of $5.5 million over the last 22 years to support underrecognized female artists over age 40. It is called Anonymous Was a Woman, in reference to a line in Virginia Woolf’s “A Room of One’s Own,” to pay tribute to female artists in history who signed their paintings “Anonymous” so that their work would be taken seriously.

The donor behind the prize wanted to remain unknown. But now she is stepping out from behind the curtain: Susan Unterberg, herself a once underrecognized female artist over 40. In a recent interview at her Upper East Side home, she said she has decided to come forward so that she can more openly argue on behalf of women who are artists, demonstrate the importance of women supporting women and try to inspire other philanthropists.