Kaitlyn is found sobbing. When you ask her what's wrong, she will tell you that her younger brother, Bevin, is missing and she can't find him anywhere. The Warden can offer to look for him, which opens the A Missing Child quest. When Bevin is found, he will go to the Village Chantry to be with his sister during the siege (see The Attack at Nightfall). You can find both Kaitlyn and Bevin back at the Redcliffe Chantry.
If the player abandons Redcliffe, she will be encountered as a walking corpse within Castle Redcliffe's dungeon.
Depending on the choices you made regarding her side quest, she may or may not play a part in the Epilogue. She may marry Teagan Guerrin. If the Warden paid Kaitlyn for her grandfather's sword enough to travel to Denerim, she uses the small fortune to open a foundry, becoming wealthy and respected. She then meets Bann Teagan at court by chance, and they marry months later. This can only happen if the Warden pays before the Attack at Nightfall quest.