Millie wrote several books under her own name of Mildred A. Wirt which were not a part of any series: Sky Racers, Carolina Castle, Couragous Wings, Linda, and Pirate Brig. She wrote two volumes under her own name for the Cupples & Leon Mystery Books for Girls series, The Twin Ring Mystery, and Mystery of the Laughing Mask.

Linda, published in 1940, involves a self-absorbed girl, Linda Calvert, who lives in Ohio and is motherless. Her father owns a golf course and she golfs. She is sent to visit relatives for the summer in Iowa. After a series of events, she becomes a respectable young woman.

Both Sky Racers and Courageous Wings, were published by the Penn Publishing company which later became Books, Inc of New York. These stories were published in 1935 and 1937 respectively. Both books involve aviation stories.

Carolina Castle is one of the harder Millie books to find, especially with a dust jacket that is intact. The story is about a girl, her brother, and the girl's friend who explore an old mansion. In the tunnels of the house they find an old trunk with a diary in it. The diary describes what was happening within the house during the revolutionary war. It's a nice story with historically accurate facts. Collector Jim Towey makes nice authorized reprints of this book!

The Twin Ring Mystery and Mystery of the Laughing Mask, are part of a 10 book Mystery Stories for Girls series published by Cupples & Leon. Shown above are two color variations of the dust jacket for Twin Ring Mystery. Titles of the series: :

• The Jade Necklace by Pemberton Ginther, 1932
• The Thirtheenth Spoon by Pemberton Ginther, 1932
• The Secret Stair by Pemberton Ginther, 1932
• Door in the Mountain by Izola L. Forrester, 1932
• Secret of the Dark House by Frances Y. Young, 1934
• The Twin Ring Mystery by Mildred A. Wirt, 1935
• The Dormitory Mystery by Alice Anson, 1937
• Mystery of the Laughing Mask by Mildred A. Wirt, 1940
• Escape by Night by Alice Anson
• Mystery of the Jade Idol by Anna Andrews Barris, 1943

Mystery stories:

Secret of the Dark House: Jean's inquiring mind and the mystery surrounding a hue dark house, combined with an alarming succession of robberies and the queer actions of a secretive old man make this a thrilling mystery story for girls. The Twin Ring Mystery: A fascinating tale of the missing half of a twin ring found in an unclaimed trunk after a sea wreck off the Florida cost. The Dormitory Mystery: The queer dark dormitory at Central University is far removed from Martha's conception of college life. Suddenly in six thrill packed weeks she is plunged into a mystery that involves twin silver oak-leaf pitchers, a strange granite toad and a fortune in missing jewels. The Secret Stair: The "Van Dirk Treasure", a jewelled and illuminated manuscript, vanishes suddenly from the old family mansion where Sally Shaw goes to live. Its recovery makes a fascinating story. The Jade Necklace: When Roslyn Blake loses her necklace of ancient Chinese design, strange events follow swiftly but Roslyn's perseverance helps her to solve the mystery. The Thirteenth Spoon: Twelve famous Apostle spoons, an the thirteenth, the Master Spoon vanish. Carol's courage solves the mystery in an original and exciting story. Door in the Mountain: Adventure hiding in strange places and an ancient legend that concerns an entire community, prove the courage and ingenuity of the four McLeans in the wild reaches of Arizona.