The correct option is E earned at a time when aviation was still so new that many of the planes she flew were
The given sentence has one error "...aviation was still so new for many of the planes she flew..." The sentence obviously does not want to say that aviation was new for planes! Option A is incorrect because of this reason. The correct logical idiom that should be used is the 'so X that Y'. Option B, too, repeats the idiomatic error of the given sentence. Also, in B 'for', a preposition, is followed by a clause 'many of the planes were' which is grammatically incorrect. In option C, the use of 'where' is incorrect in the given context as it refers to a place and not time. Also, the demonstrative pronoun 'that' needs to be followed by a noun. The use of 'so new such that' (it should be 'so new that') in D is incorrect as is the use of 'in which' to refer to a point of time ('when' is used to refer to time). Thus, option E is the only correct option that befits the context.