“Arianrhod’s themes are the arts, magic, manifestation and rebirth. Her symbol is a silver wheel (spinning tools i.e. shuttle, yarn). In Welsh tradition, this is the Goddess of the ‘silver wheel’ upon which magic is braided and bound together into a tapestry of manifestation. Stories tell us that Arianrhod abides in a star where souls wait for rebirth (the wheel here becomes the wheel of life, death, and rebirth).
Known as Catherine of the Wheel, Saint Catherine of Alexandria oversees spinsters (literally and figuratively). Like Arianrhod, she is a patroness for lace makers and seamstresses. In keeping with this theme, today is an excellent time to try your hand at making a special pouch for housing some of your magical tools or trinkets. Begin with two rectangles of natural-fiber cloth one inch larger than the item you wish to house within. Put the right sides together and stitch three edges, leaving a three-quarters of an inch opening at the top for a drawstring or finished edge. Turn the pouch right side out. Repeat the Goddess’s name to bind Arianrhod’s power in each stitch. Fold over the top hem twice so it won’t unravel, and stitch that with silver thread for the Goddess’s protection.
If time doesn’t allow for this, a favored beverage to inspire this Goddess’s blessings is ale or cider with an apple slice or caraway bread and tea. Pour a little of this out as a libation, then drink it fully to awaken and energize Arianrhod’s magical potential within you.”
(Patricia Telesco, “365 Goddess: a daily guide to the magic and inspiration of the goddess”.)
Arianrhod (ah-ree-AHN-rhohd) is “the Goddess of the ‘silver wheel’ [and] was a Welsh sorceress, who, surrounded by women attendants, lived on the isolated coastal island of Caer Arianrhod. Beautiful and pale of complexion, Arianrhod was the most powerful of the mythic children of the mother Goddess Dôn.
It was said that She lived a wanton life, mating with mermen on the beach near Her castle and casting Her magic inside its walls. She tried to pretend virginity, but a trial by the magician Math revealed that She had conceived two children whom She had not carried to term: in leaping over a wizard’s staff, Arianrhod magically gave birth to the twins Dylan-son-of-Wave and Llew Llaw Gyffes. Dylan slithered away and disappeared. Arianrhod’s bother, the poet Gwydion, recognized the fetus as his own child, born of his unexpressed love for his sister.
Gwydion took the fetus and hid it in a magical chest until it was ready to breathe. Arianrhod, furious at this invasion of Her privacy, denied the child a name or the right to bear arms – two prerogatives of a Welsh mother – but Gwydion tricked Arianrhod into granting them. Eventually the Goddess overreached Herself, creating more magic than She could contain; Her island split apart, and She and Her maidservants drowned.
Some scholars read the legend as the record of a change from mother right to father rule, claiming that the heavenly Arianrhod was a matriarchal moon Goddess whose particular place in heaven was in the constellation called Corona Borealis. The argument has much in its favor, particularly the archetypal relation of Arianrhod to Her sister moon Goddesses on the continent, who like Artemis lived in orgiastic maidenhood surrounded entirely by women. Other scholars, unconvinced that the Celts were matriarchal at any time, see Arianrhod simply as an epic heroine” (Monaghan, p. 53).
Upon reading Her story, my initial reaction was “Damn…that’s pretty cruel and spiteful.” But as Claire Hamilton in her piece entitled “Arianrhod – Bad Mother or Mythic Goddess?” points out, “If Arianrhod really is the great mother of the Sacred King child, then why does She seem so vindictive? What are these so-called curses about? Why does She seem to be denying Her son his rights? And why is She so powerful that Gwydion has to work so hard to outwit Her? In addressing these questions, we should first bear in mind the strong possibility that by the time Her tale was written down by the Welsh monks, they had spotted Her pagan power and decided to deliberately slander Her name.”
Hamilton sums up her entry by stating, “I believe that Arianrhod can be seen not as a furious and vindictive woman, but as a powerful and wise matriarch. A mother who truly understood the needs of her son, and the sacred requirements of Her maternal role, and who was not afraid to use Her Crone power to secure them. And for these reasons, I believe that the wonderful Goddess Arianrhod, the beautiful woman whose feet rest on the crescent moon, and whose head is ringed with stars, is a hugely important figure in Welsh myth, and a deeply inspirational model for all mothers today.”
“Arianrhod is said to be able to shapeshift into a large Owl, and through the great Owl-eyes, sees even into the darkness of the human subconscious and soul. The Owl symbolizes death and renewal, wisdom, moon magick, and initiations. She is said to move with strength and purpose through the night, Her wings of comfort and healing spread to give solace to those who seek Her.” 
Below is a list of associations that I put together from a few different sources that I could find:
Pantheon: Celtic (Welsh)
Elements: Water, air
Associated Planet: Moon
Colors: Blue, purple, grey, silver, white
Symbols: Triple Goddess, wheels, spinning tools, the silver wheel, the zodiac, nets, the full moon, Corona Borealis, Oar Wheel (a special boat that carries dead warriors to Emania, or the Moon Land)
Areas of Influence: Reincarnation, fertility, female power, sovereignty, fate, beauty, past life memories, difficulties
Sacred Animals: Owls, wolves
Suitable Offerings: Silver coins, wheat, candles (green and white).
Sacred Tree: Birch
January 12: Day of Arianrhod: Welsh Celtic holy day. Day of Arianrhod (Welsh) Goddess of reincarnation, the Wheel of the Year, the full moon, fertility, and female power. Often portrayed as a weaver [of spells], She is linked to lost creation myths. — Celtic information provided by Shelley M. Greer ©1997.
February 14: Arianrhod steps over the magical wand of Math: Celtic holy day. Arianrhod steps over the magical wand of Math, which manifests truth, to prove her virginity. The wand causes the seed of her lover, which is in her womb, to ripen, grow and give forth in an instant, giving birth to Dylan Ail Ton, whose name means “Sea, son of Wave”. Dylan makes straight for the sea, and is accidentally slain by his uncle Gofannon. Her brother, Gwyddion, snatches up the after-birth to incubate Llew Llaw Gyffes, the great archer. — Celtic information provided by Shelley M. Greer ©1997.
December 2: Festival of Arianrhod: Welsh holy day. The Goddess descends on a silver chariot to watch the tides. 
Hamilton, Claire. Goddess Alive!, “Arianrhod – Bad Mother or Mythic Goddess?”
Monaghan, Patricia. The New Book of Goddesses and Heroines, “Arianrhod”.
Rainbowpagan. Youtube.com, “Goddess Arianrhod“.
Thewhitegoddess.co.uk, “Arianrhod – Goddess of the Silver Wheel“.
Bianca. Orderwhitemoon.org, “Arianrhod, Goddess of the Milky Way“.
Celtnet.org.uk, “Arianrhod, A Cymric goddess: Silver Wheel, Silver Orbit“.
Journal of a Poet, “Arianrhod, Moon Goddess of the Silver Wheel“.
LadyRavenMoonshadow. Sacredmistsblog.com, “Goddess of the Week: Arianrhod“.
Shaw, Judith. Feminismandreligion.com, “Arianrhod, Celtic Star Goddess“.
Sisterhoodofavalon.org, “The Goddesses“.
Skye, Michelle. Goddess Afoot!: Practicing Magic with Celtic & Norse Goddesses, “Meeting Arianrhod, Welsh Goddess of the Stars” (p. 23 – 31).
Took, Thalia. A-Muse-ing Grace Gallery, “Arianrhod“.