“Gujeswari’s themes are Earth, water, abundance, offering and prayer. Her symbol is a bowl of water. Gujeswari is a potent Nepalese Goddess of Earth and all its bounty, and today is Her festival day, known as Gujeswari Jatra. In many temples, the Goddess’s presence is represented by a simple bowl of water, the life-giving substance and purifier of body, mind and spirit.
Buddhists and Hindus in this region honor the mother Goddess Gujeswari today by giving Her offerings, usually preceded by fasting and prayer. Follow this example, and put a bowl of fresh water on your altar or a special place where it won’t be disturbed for the day. If physically feasible, abstain from eating one meal today to honor the Earth and Gujeswari’s goodness by returning (or preserving) some of that bounty. Otherwise, simply abstain from a favorite food for the day as a kind of sacred sacrifice.
At the end of the day, just before you go to bed, sprinkle the water from the bowl around your living space. First, go counter-clockwise to banish negative energy that hinders free-flowing blessings. Then go clockwise, allowing Gujeswari’s water to cleanse and renew the ambiance in every room. If you have some left over, sprinkle your pets (for health), your car (for safety in travel), and children’s beds (to protect them from nightmares), and dab some on mechanical objects to keep them working smoothly.”
(Patricia Telesco, “365 Goddess: a daily guide to the magic and inspiration of the goddess”.)
I really couldn’t find anything on today’s Goddess or the festival; it seems as if this Goddess and festival are some big secret. The only information I could find was on a temple called Guhyeshwari Temple, that I had initially assumed would be dedicated to Her. ”Guhyeshwari Temple, also spelled Guheswari or Guhjeshwari, is one of the revered holy temples in Kathmandu, Nepal. This temple is dedicated to Adi Shakti. This refers to the popular legend where Shiva distressed was carrying the corpse of Devi Sati and Vishnu annihilated it with his Sudarshan Chakra. Shiva later declared the 51 such places where Devi Sati’s body parts fell to be worshipped as the Shakti Peethas and meditated at all these places as various forms of Bhairavas. The place where Devi Sati’s knees fell is Guheswari in Kathmandu. In Nepal the form of Shakti is Mahashira and the form of Bhairava is Kapali. King Pratap Malla built this temple in the 17th century.
The temple name originates from guhya (cave) and ishwari (goddess). Non-Hindus are not allowed to enter this temple.
In another piece I read on nepal.com, it states: “The two main religions in Nepal are Hinduism and Buddhism and very often worshipers from the two faiths intermingle at temples and shrines. This sort of interfaith is practiced throughout the country though really each person is worshiping his or her equivalent of the god to which the temple or shrine is dedicated. There are a few exceptions to this intermingling of believers though and the Guheswari Temple is one of them. The temple is strictly a Hindu temple and all non-Hindus – whether the person is Christian, Buddhist or from some other faith – are not allowed access to the temple courtyard let alone the temple itself.
The Guheswari Temple in Nepal is a very sacred temple which is dedicated to the Goddess Parvati. The name ‘Guheswari’ is sometimes also spelled ‘Guhyeshwari’ or ‘Guhjeshwari’. The temple has a strong sexual connotation that is not only linked to its fabled beginning but also to its name. According to legend the wife of Lord Shiva, Parvati, sacrificed Her life by burning Herself to death in Her father’s ritual fire. Her distressed husband then chose to wander the world, carrying the body of his dead wife as he did so. As he passed over the spot where the Guheswari Temple is located today it is said that Her ‘yoni’, or female sex symbol, fell to the earth. In the 1653 King Pratap Malla saw fit to restore the magnificent Gushewari Temple. This temple represented the female force that Parvati was the very embodiment of.
The Guheswari Temple is located in Kathmandu not far from the Pashupatinath Temple. The actual temple does not house any images of the legendary Goddess but there are a lot of other things here worth seeing. The building is ornate and beautiful and the worship of the people here is usually very sincere and touching. Many believe this to be the temple to go to in order to pray for marital fidelity and a lot of different Hindus will make the trip here to ensure that their marriages do not suffer.” 
Several other articles I read also said that this is where Her yoni had fallen. This makes more sense to me as when you break Guheswari down: guhya (cave) and ishwari (goddess) – the cave is a very earthy and primordial symbol of the womb; which is exclusively female – making it a female force. Also, I found that ”devotees offer wine, eggs etc. in a holy orifice which has been regarded as the place of worship since times immemorial.”  Again, eggs being a very feminine symbol and this holy orifice symbolizing the yoni.
So, in conclusion, I do not believe that Gujeswari is a Goddess per se, but more of a primal force, aspect or attribute of Parvati, who is considered as complete incarnation of Adi Parashakti (who is considered to be truly spirit without form - the Great Divine Mother Goddess, the source of all other Goddesses). Good stuff to wrap your head around, eh?
Geneeyuss-placesofpilgrimageofnepal.blogspot.com, “GUHESWARI TEMPLE“.
Nepal.com, “Guheswari Temple“.
Wikipedia, “Guhyeshwari Temple“.
Nkdedhann.com, “List of 51 Shakti Peetha of Goddess Durga“.
Wikipedia, “Adi Parashakti“.
Wikipedia, “Mother Goddess [Hinduism]“.