The difference between 'would have' and 'will have' in this sentence is tense.
is conditional, indicating that in order for her to have saved the money, something else must have taken place first. For example:
She would have saved . . .
"She would have saved enough money by the time she retired, but her salary was cut in half for three years."As you can see, the above sentence is past tense. Now let's look at the alternative.
is subjunctive, indicating that if all goes according to the present plan, she will, in the future, have saved the money. Even though I use the word 'if', this is not conditional, because it is expected that all will go according to plan.
"She will have saved . . . "
"She will have saved the money because she is investing a certain amount from every paycheck she receives, and because she is a very shrewd businesswoman."In this example, we're discussing her in the present tense, predicting an action that will take place in the future.