The correct answer is "She doesn't need help". The reason why it's so is because the word doesn't is for singular purposes, and the subject in question is a single person only - which is "she". Therefore, it's a Standard English language that's in use as a sentence.
I believe it is both a and b, since both would be good. hope this helped!
I think that it is:
A.
Adults cannot appreciate the beauty of the natural world as children can.