Complex sentence: The name Idril was a Sindarized form of her Quenya name "Itarillë" (or "Itarildë"), which means "sparkling brilliance" seemingly related to the fact that she was a lovely blonde; and inherited her hair colour from her Vanyarin mother.
Split into simpler sentences: The name Idril was a Sindarized form of her Quenya name "Itarillë" (or "Itarildë"), which means "sparkling brilliance". She was a lovely blonde; she inherited her hair colour from her Vanyarin mother.