Happy Birthday greeting cards for centenarians are not always easy to find. But that didn't stop people from combing area shops to find just the right one for Wilhelmina Audesirk.

Audesirk, known as Mina to her friends, turned 100 July 10, and she celebrated with those who mean the most to her -- her younger sister, Emma, 92, and her buddies at Anne Arundel Medical Center, where she has been a volunteer since 1975.

Even now, Audesirk, who has always lived with Emma -- the two of them never marrying -- delights in showing up at the hospital monthly to work on nonmedical tasks.

Her volunteer work includes stuffing envelopes and crocheting hats for newborns. She estimates that she has clocked more than 14,000 hours since joining the hospital's Office of Auxiliary, which oversees the volunteers.

Audesirk, a neat woman with a sense of humor and very good health, is the oldest of the auxiliary's 750 volunteers and one of its most dedicated.

So to honor her, the hospital gave her a big birthday party.

"Mina has struck me most as someone who never complains, always very positive, always with a sense of humor," said Lisa Hillman, executive director of the Anne Arundel Medical Center Foundation. "She has always appreciated volunteering because she knows not only is she helping us to make money, but she helps us to save money."

It is not just Audesirk's work ethic that Hillman admires. Both Audesirk and her sister, Hillman said, possess a steely determination, independence and energy that make them well liked among the volunteers.

The sisters, who do everything together, have traveled to every state except Texas. They grew up in New Jersey -- they also had four brothers -- and moved to Maryland after retiring many years ago.

They live in a two-bedroom apartment with a view of the Bay Bridge and a green shag carpet.

Audesirk, a retired secretary, and her sister are too old to drive. Every month the medical center foundation sends a driver to pick them up and bring them to the hospital. They spend four to six hours stuffing envelopes with fundraising letters and donor correspondence.

"Mina's very nimble with her fingers. She's able to fold, to stuff an envelope, to seal it, to see the name and address," Hillman said of Audesirk's volunteer work.

"Essentially, she is still working at 100 years old."

It helps that Audesirk knows many people in the area and is able to help the foundation update its mailing lists by pointing out residents who have moved or died.

"She's like a one-person mailing machine," Hillman said.

At the height of her volunteer work, Audesirk served as president of the auxiliary, a good fit for her strong office skills. She boasts she can still take dictation, write in shorthand and type 140 words per minute.

She also can crochet.

With a record-breaking 5,000 babies born to date this year at the hospital, the tiny pastel-colored hats come in handy.

Audesirk said she can make a baby hat in about four hours, despite some mild arthritis in her fingers.

In addition to her hospital volunteer work, Audesirk plays bingo every week with other senior citizens in Edgewater.

She also enjoys reading and baking, especially her favorite -- chocolate cake, from the traditional layer version to her current favorite, chocolate mocha Bundt cake.

Audesirk said her mother taught her how to bake when she was 7 years old. This is one of many lessons, including what she's learned from living such a long life, that she enjoys imparting to others.

"Keep busy and don't ever feel sorry for yourself," she said. "Because there's plenty of people that are worse off than you."

The Audesirk sisters, Emma, 92, left, and Wilhelmina, or Mina, 100, volunteer at Anne Arundel Medical Center.