B). Her hair is smooth, straight, and long.
A few key words helps us understand that her hair is smooth, straight, and long. These are “silk”, “sheet”, and “flowing down her back”.
“Silk” helps us imagine the hair as smooth, and soft.
“Sheet” and “flowing down her back” helps us imagine it as long, and straight down her back.
Why it isn’t the other answers:
A). Although she might enjoy brushing her hair, in no way is it mentioned in the sentence.
C). This one puts the main subject on her back, which the sentence is describing her hair.
D). The sentence is describing her hair, as stated “Her blond hair...”. This choice would be taking the description too literally, and ignoring that her hair is the main subject.
