I like it. I'd pronounce it like, I guess ɹoʊz-ə-leɪn? Basically "
Rose" (emphasized) and then "
Elaine" but with a schwa for the first "e".
I don't know if its origin was just a
Renesmee type thing, but it feels like an established/vintage variant along the lines of
Madelaine as a variant of
Madeline (it fits that same pattern with
Rosaline).
I like
Elaine better than
Ellen because the vibe seems more medieval to me (even though
Ellen was literally a medieval name!).
Rosarya maybe? Rosenya / Roseithne? (I tried to "make up"
Rosalia but it's already a name :P)