Mab, was the youngest of the three Legendary Fae Queens, alongside Maeve and Mora. After her death it was presumed she was proclaimed a goddess: known as Deanna. Whether or not this is true is unknown. However in most of the cases as mentioned in the books (see below), Mab and Deanna are described as one being. She is the founding ancestor of House Ashryver of Wendlyn, and her descendants have inherited their magical powers after her.
It was stated in Heir of Fire she had fair hair.
Before the Valg Queen Maeve and later on the three Valg Kings, arrived, Erilea was occupied by the faeries and the Fae. In the immortal lands of Wendlyn and Doranelle, the faeries and Fae were ruled by Mab and her older sister Mora. The fair-haired Mab, the youngest, who bore the shape of a white swan, and cunning Mora, who bore the shape of a great hawk.
When Maeve reached Erilea and arrived at Wendlyn, she saw that the Fae were ruled by Mab and Mora as Sister-Queens. Unbeknownst to Mab, Maeve ripped into her and Mora's minds, making them believe that they always had an older sister, Maeve. An unknown time following Maeve's installment as a fellow Queen of the Fae, the Valg Kings - Orcus, Mantyx and Erawan - arrived at Wendlyn, searching for their Valg Queen. But Mab, Mora and Maeve battled the three Kings each, while their Fae armies dealt with the Valg hoardes. Once the first Valg Wars ended, with Maeve banishing Orcus and Mantyx, peace returned to Erilea.
Some time in Mab's life, she fell in love with a human prince. Alongside her human mate, she founded the Kingdom of Wendlyn, ruled by House Ashryver, their descendants.
Mora, fell in love with a mortal as well. Naturally, Maeve disapproved of their actions, and it has been stated that both sisters gave up their immortality to live shorter lifespans with their mates while simultaneously evading Maeve's wrath. Some presume that the two Fae Queens were loved fiercely by their human mates, and so they became mortal too, having tied their fates with their mates.
After her death, Mab was presumed to be proclaimed as a goddess, known as Deanna.
In Crown of Midnight, Chaol states that Mab had been made into a goddess, known as Deanna, Lady of the Hunt. He remembers a memory of Celaena feeling uncomfortable at recieving the golden arrow of Deanna, of her great-grandmother Mab.
In Heir of Fire, the following is mentioned about Mab/Deanna. Chaol muses on Celaena's skills as being similar in her Ashryver bloodline, with Aedion - due to their great-grandmother being Mab, who was crowned as Deanna in the recent generations. Celaena states that although Mab was immortalised into godhood thanks to Maeve, Mala had a sister in the moon long before Mab took her place. Rowan tells her that Deanna was the original goddess, and mortals had given her some of Mab's traits.
In Queen of Shadows, Aelin specifically mentions that Deanna was her own ancestor.
Whether or not she merged with the original Goddess of the Moon, or replaced her, is unknown. However it is known from the books that Deanna is related to Aelin.
Empire of Storms
It was mentioned by Maeve, that her bloodline ran true, so that all her descendants who inherited her full powers and shifting abilities would gain her immortality upon Settling, as well. Aelin would go through the Settling in around 5 years, as would Aedion, at an sooner time perhaps.
Before sacrificing her immortality to live with her human prince (possibly her mate), Mab was a full-blooded Fae, with all the standard abilities of the Fae.
Secondary animal form - White Swan.
Magic - Water Magic. It was mentioned that House Ashryver inherited their magical powers from Mab. Since Aelin's mother was shown to have water magic, Mab is assumed to be a full water-wielder.
Alongside her standard water abilities, she is also immensely affiliated with her element. This is her "Water Affinity", reminding the bearer of their salvation, and their self-preservation. Even a drop of her magic grants the user healing abilities. This is where Aelin Galathynius gets her healing powers from. Since Mab had the full powers of her Water Magic, she would have had immense healing abilities, though not as strong as Silba's healing powers.
- Her traits seem to heavily resemble those of the Hindu Goddess Saraswati:
- Saraswati is the divine manifestation of the river Saraswati (and water), similar to how Mab had water magic
- The Goddess is heavily associated with a white swan, as her mount/associate - Mab's secondary form is a white swan
- She is revered as the Goddess of purity, healing and creation, where her water gives life - similar to Mab regarding her Water Affinity.
 - Sarah J Maas's Pintrest board - pin of Mab <https://au.pinterest.com/pin/246853623301794045/>