Marianne Frey

Marianne Frey is one of the many granddaughters of Walder Frey. She only appears in the Season 3 episode "The Rains of Castamere".

Background
Marianne is one of the many granddaughters 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 books, there's a granddaughter of Lord Walder named Marianne Vance, daughter of Ser Dafyn Vance and Maegelle Frey. She's among the Frey girls presented to Robb before Edmure's wedding.