A female deity of the ancient Maya was a goddess known as Ix Chel, (also known as Lady Rainbow), who was either the companion or wife of Itzamná (God D). So far as it is understood, Ix Chel seems to have two forms: one that is also known as the old (or aged) moon goddess (Goddess O) -- called either Chac Chel (Chak Chel) or Chakal Ix Chel -- and one that is known as the young moon goddess.
The apperance of Ix Chel varies depending on the aspect. Maya scribes drew the young aspect of Ix Chel was a young and beautiful woman who has a large nosepiece, and was seen with a rabbit and a crescent moon. The aged aspect of Ix Chel was depicted as an old woman with snakes in her headdress and jaguar paws for hands, who often is pouring water out from a jar.
Ix Chel seems to have both positive and negative functions. Her positive functions included being the goddess of divination and weaving as well as a medical goddess of healing, childbirth and medicine. Her negative functions included being a goddess of floods and destruction (and at times war), as well as of snakes. However she does not bring sickness.
This goddess was important along the Carribbean coast. A shrine to Ix Chel can be found on Cozumel Island, in which a statue may have been designed so that a priest could make it seem like the statue "talked".
Sources including Handbook to Life in the Ancient Maya World (published by Oxford University Press) and Dr. Chuchiak -- say that Ix Chel was a moon goddess. However, in Mesoamerican Mythology:
A Guide to the Gods, Heroes, Rituals, and Beliefs of Mexico and Central America (also published by Oxford University Press) states that Ix Chel may have been a moon goddess.
Goddess I and the Tonsured Maize God
Goddess I may have been connected connected to the Tonsured Maize God. There are images that show her looking somewhat like the Tonsured Maize God, wearing his costume, hairstyle and having his facial markings. Another possible piece of evidence for the connection is an image showing a crescent moon in connection to the Tonsured Maize God.
In Yaxchilán there is a depiction of a ruler's parents in which an image of his father has a sun glyph in it while an image of the ruler's mother has a lunar sign in it. This is what, according to Handbook to Life in the Ancient Maya Word, gives evidence to a theory that Ix Chel was the wife of the sun god.
Other Possible Aspects
Dr. John F. Chuchiak IV -- the Assistant Professor of Colonial Latin American History at the Department of History at SMSU -- states that Goddess I was confused with another goddess (who he designates as I'). This other goddess, named Sakal Ix Chel that was was similar in appearance with Chac Chel. Though he is not entirely sure, he thinks it is possible that Sakal Ix Chel is the same as Chac Chel.
Also, there is a theory that states that Blood Woman -- or Blood Moon -- (called Xkik in Handbook to Life in the Ancient Maya World) could be an aspect of Ix Chel. Blood Woman was the mother of the Hero Twins.
Missouri State University: MAYA GODS AND GODDESSES
"Mesoamerican Mythology: A Guide to the Gods, Heroes, Rituals, and Beliefs of Mexico and Central America"; Kay Almere Read, Jason J. Gonzalez; 2002
"Handbook to Life in the Ancient Maya World"; Lynn V. Foster; 2005
"The Ancient Maya: New Perspectives"; Heather Irene McKillop; 2004