She probably would have at least tried to befriend her and I feel like they would have gotten on with how you speak of her. This backscene MUST happen. Lillie is kind of a romantic sap, and especially back then as she was a teenager so she would DEFINITELY encourage him. She would totally tell him to just go for it and find the whole thing incredibly romantic.
Also depending on how close the girls were she might have maintained contact with her after she moved away with Talfryn via letters, at least until the siege.
Imenry so far likes and respects Talfryn and she forgives him for thinking of her as a barbarian. After all other people have actually called her that to her face and well, it's sort of accurate I suppose XD.