If you mean the girl with blue hair, which you meet during the main story, and who is part of Raziel's group, then she can't be found anywhere anymore at the current end of the story.
That's Jaylin. You can find her in the jewelry store in Thremten after advancing Kayelinth’ events far enough. Her CG scene can be started afterwards at the Amaranthe beach.
The walkthrough shows all CG room pages and where to meet the characters. ;)
