But she quickly learned the baseball great is a revered figure among collectors, and the most sought-after baseball card in history. And thanks to an unexpected donation, one of the century-old cards belongs to Muller and her order, the Baltimore-based School Sisters of Notre Dame.
The sisters are auctioning off the card, which despite its poor condition is expected to fetch between $150,000 and $200,000. The proceeds will go to their ministries in 35 countries around the world.
The card is part of the T206 series, produced between 1909 and 1911. About 60 Wagner cards are known to exist.
A near-mint-condition T206 Wagner card sold in 2007 for $2.8 million, the highest price ever for a baseball card. Muller remains aghast that the 1 1/4-inch-by-2 1/2-inch piece of cardboard could sell for even a fraction of that.
"It just boggles your mind," Muller told The Associated Press. "I can't remember a time when we have received anything like this."
The brother of a nun who died in 1999 left all his possessions to the order when he died earlier this year. The man's lawyer told Muller he had a Honus Wagner card in a safe-deposit box.
When they opened the box, they found the card, with a typewritten note: "Although damaged, the value of this baseball card should increase exponentially throughout the 21st century!"
The card was unknown to the sports-memorabilia marketplace because the nuns' benefactor had owned it since 1936.
It has a big crease in the upper right-hand corner, and three of the white borders have been cut off. It has also been laminated. But even in poor condition, a T206 Wagner card is prized by collectors, said Chris Ivy, director of sports auctions at Heritage Auction Galleries in Dallas, which is auctioning the card.
"The T206 set is known as 'The Monster' among collectors. It's just really tough to complete the entire set," Ivy said. The Wagner card is "one of those that's always sought-after, always desirable, and there's not a big population of them. Even in a lower grade, they do have quite a bit of demand and command a strong price."
Wagner, nicknamed "The Flying Dutchman," played for 21 seasons, 18 of them with the Pittsburgh Pirates. He compiled a .328 career batting average and was one of the five original inductees into baseball's Hall of Fame.
The card was printed during the prime of Wagner's career, but the American Tobacco Company ended production soon after it began. Some say Wagner didn't want to promote tobacco products to children. Others believe it was a dispute over money that led to the card being pulled.
On the card, Wagner appears stocky and pale, with his hair parted down the middle and the city on his jersey misspelled: "Pittsburg."
The auction ends Nov. 4, and the highest bid was $60,000 as of Wednesday morning.
Muller is making frequent checks to the Heritage Auction Galleries website - an unusual practice for someone who's taken a vow of poverty. But potential bidders should know that the sale of the card will help people worldwide.
"The money that we receive from this card will be used for the many School Sisters of Notre Dame who are around the world, who need support for their ministries for the poor," Muller said.