Unless you already know what a relative clause is, you are not ready to do this lesson. Review relative clauses by clicking on the link at the top of this page. When you have finished, return and continue.
Pronouns rarely get modified ("that not impossible she" or "she who must be obeyed"). If it happened more often, everyone would get more practice with it and there would be less confusion. As it is, though, even best-selling novelists make mistakes.
Here is the whole lesson in a nutshell: When two pronouns stand side by side, as in "she who," the case of each one of them is completely independent of the other because they belong to different clauses. That means that there is absolutely no way to find one "right" pattern for all sentences involving these pronouns. Some sentences will require "her who," others "she whom," others "she who," others "her whom." The only way to get it right every time is to read the sentence from the inside out.
By this is meant that you should figure out the structure and form of the relative clauses (the ones beginning with the "wh-" words) separately from the independent clauses in which they are embedded (and I recommend doing them first). This is what this lesson will teach you to do.