Blythe Rosemarie is lovely.
Blythe is one of those names that always surprises me in how much I like it, because I never think about it. Whenever I come across it, it feels breezy and refreshing in a sweet vintage way.
Bly feels a little too short for a first name, but I like it as a nickname option. I also like the connection with the classic ghost story The Turn of the Screw (and it's most recent incarnation, The Haunting of Bly Manor).