Shirei Frey

Shirei Frey is the youngest daughter of Walder Frey. She only appears in the Season 3 episode "The Rains of Castamere".

Background
Shirei is the youngest daughter of Walder Frey, the Lord of the Crossing.

Season 3
Along with several of Lord Frey's other daughters and granddaughters, Robb Stark had the option of marrying her. When he arrives at The Twins for his uncle Edmure's wedding, Robb apologises for his slight against them.

In the books
In the A Song of Ice and Fire novels, Shirei Frey is the - supposed - seventh daughter of Lord Walder Frey. She is the second daughter of Lord Walder Frey and his seventh spouse, Lady Annara Farring. However, according to Merrett Frey, Black Walder Frey was rumored to be sleeping with Lady Annara, thus casting doubts on the parentage of her children. She is six years old.