Mrs. Yoop - The first Yookoohoo encountered in the series, specifically in Tin Woodman, she's the wife of Mr. Yoop, a giant who was captured and caged in the Quadling Country. His wife escaped this same fate by turning herself into a mouse until the captors had left. She claims that nothing she transforms ever regains its original form, but since she turned herself back from her mouse form, that's obviously not true. When she transforms the Tin Woodman, the Scarecrow, Woot the Wanderer (who predates the Internet by some time, so his name doesn't indicate that his parents were 1337), and Polychrome, Ozma manages to reverse most of these changes (the first real magic she works in the series without the Magic Belt). She's unable to change Woot back from a green monkey, though, so she transfers the form over to Mrs. Yoop herself. Now that's what I call poetic justice! Mrs. Yoop also has (or at least had) a lace apron that could open doors, and the ability to read minds if she wants to. Her first name is never given in the official books, but Fred Otto's short story "The Fate of the Yoops" calls her Ali. (Get it?) And in "Time Travelers in Oz,", which provides some background for the character, her first name is Moyna.
Reera the Red - In Tin Woodman, Ozma says that she thinks Mrs. Yoop is the last Yookoohoo remaining in Oz, but it turns out that she doesn't know about Reera. This isn't too surprising, as Reera is a hermit, living in a corner of the Gillikin Country with a few animals to keep her company. Since she keeps changing their forms, we don't really know what they are naturally, although later stories featuring Reera makes one a donkey and one an ant. Her title comes from her red hair, but since she usually appears in other forms, this fact is generally not readily apparent. Ervic the Skeezer tricks her into restoring the Three Adepts to their natural forms, but she doesn't really mind once the trick is revealed. A fan-written book, Red Reera the Yookoohoo and the Enchanted Easter Eggs of Oz, has Reera settling down to married life with Prince Glenn of Portmore, and she also puts in an appearance in Edward Einhorn's The Living House of Oz (with no sign of any husband, so maybe the marriage didn't work out so well).
Now, on to some other female magic-workers:
Gayelette - One interesting aside in the very first Oz book is the story the King of the Winged Monkeys tells about how his people (well, primates, anyway) came to be slaves to the Golden Cap. It was the work of a reputedly good but dangerously bad-tempered sorceress named Gayelette, who was angry that the Winged Monkeys had ruined her fiancè Quelala's clothes on their wedding day. Wow, talk about a bridezilla! Anyway, we don't know how long before the main story this took place, but it's apparently been some time, as the King of the Winged Monkeys back then was the grandfather of the one in Wizard. Then again, it's not like we know what the normal lifespan is for a winged monkey. The fact that Gayelette is described as living in the north has led some to speculate that she might actually be the same Good Witch of the North who met Dorothy at the beginning of the book, but there's no real indication of this, and it contradicts what's later revealed in Giant Horse. Gayelette was ignored throughout the rest of the canon, but several apocryphal books have featured her as a character, including Roger Baum's Dorothy, March Laumer's Frogman, and Dennis Anfuso's Winged Monkeys.
Maetta - She seems to play the same role for the Land of Mo that Glinda does for Oz, being the one to whom the people of Mo turn when they have problems they can't solve themselves. Timtom went to Maetta to get a cure for Princess Pattycake's bad temper, and Pattycake's sister Truella flew to her castle to get some items to use in fighting the evil wizard who'd stolen her big toe. She also supplied the Monarch of Mo with a magic casket that provides different surprises every time it's opened. Interestingly enough, Maetta actually took the place of Glinda in Baum's stage version of Land, which was known as The Woggle-Bug.
The Adepts at Magic - Since the plot of Glinda is loaded with magic-workers, I've already mentioned them a few times. Just to jog your memory, after teaching magic to Queen Coo-ee-oh of the Skeezers, she betrayed them and turned them into fishes. They were eventually restored by Reera, at the behest of Ervic. Their names are Aurah, Audah, and Aujah. One has blonde hair and blue eyes, the second dark brown hair and gray eyes, and the third white hair and brown eyes. I don't think we ever actually learn which name goes with which physical features, though. They reappear in Dave Hardenbrook's Unknown Witches, in which they do have different personalities, although it's still sometimes hard to tell them apart. Dave also renames them after chess players, for some reason. Another post-canonical appearance of the Adepts is in Living House, in which Buddy visits them on Flathead Mountain.
Valynn - I'm not actually sure how to categorize her, but she's the guardian of the apple tree that preserves the magic of Oz, which stands in the garden of a castle not far from the Emerald City. When the magician Bortag tried to steal one of the apples to revive the Wicked Witch of the South, Valynn transported her castle to Limbo, but grew bored and returned after a century. And that's when the events of Enchanted Apples, which resulted in Oz being temporarily disenchanted, began to take place.
I think that's about all of the female Ozian magic-workers, except for the fairies and their ilk, who are a different sort entirely (well, aside from Faleero). If I've forgotten any, please let me know.