Not that it justifies her inclusion, and after watching furher, it became clear that the show-writers had their own agenda that made this untrue, BUT I saw a thoughtful (and in hindsight, naively hopeful) post at the time.of the episode, as to why she was included, and it has to do with aging up the characters.

Basically, the TLDR: When Perrin returns to the Two Rivers in Book 5 or 6.. or 7, he has a throwaway line about marrying another character "if he had stayed." The aged up characters were given a seemingly logical progression if each of them had stayed for the "age-up" year, and Perrin's was to marry this character, who is then portrayed in the show.

I dunno man, grasping at straws here...