The Witches’ Kitchen by Allen Williams may be the first Girls Underground example I’ve come across where the girl starts off the story as an animal, and must go through the journey to regain her human form (The Cat Returns and The Old Country both have the girls becoming animals partway through, and The Last Unicorn has the protagonist begin as an animal and get turned into a girl temporarily).
The Toad doesn’t know her name or her past when she finds herself trapped in a magical and labyrinthine kitchen by two evil witches. She is initially helped by an imp there and also picks up several other companions along the way, as she tries to both escape and discover her identity (which, when she does, reveals her to be an orphan among other things). She is pursued by magical creatures in the shape of skeletal birds, sent by the witches to retrieve her for their spell. She encounters a group of spiders whose venom gives her visions of her past life. Eventually she comes to learn that the witches themselves are responsible for her current state. After a betrayal by one of her companions (although against his will), she uses her newly-discovered magical powers to wage a final battle with the strongest witch. The Toad remembers who she is, returns to her natural form, and escapes the kitchen.
(While the writing in this book was somewhat uneven, the illustrations by the author made up for it – it’s worth checking out just for those.)