Canon Background
https://awoiaf.westeros.org/index.php/Arwyn_Oakheart

In-Campaign
Arwyn welcomed visitors from House Jasper to Old Oak in October of 285 AC. After dinner she ordered her family, retainers, and servants to leave after they shared that Lord Tyrell had asked them to assist her with a problem. She proceeded to discus a rather sensitive matter with the visitors. She shared that her young niece, Jeyne, had become pregnant out of wedlock and that as a result a betrothal was proving difficult. The following morning Teddy Jasper suggested a match with House Jasper’s captain of the guards, Jardon Pyke. Arwyn initially balked at this suggestion but eventually consented after a terse discussion.