D
before是在...时间之前,奋斗了许多年了；而since是自从...到现在,但made这个时态与现在无关,故错误；that的话就只能理解为强调句了,但是去掉It was.that后,句子是不成立的,故错误；when是“当...的时候”,词义错误,它无法表明was这个状态的时间.
若强调句的话应该说：It was for many years that she made.