I wouldn't give her Kingdom Come in a fit. Its continuity heavy, and a dreadful, dreadful story.
Why I Hate Saturn is a very good choice. Even my wife, who hates comics books, really liked the conversations (and the flip at the end) in that one.
The Dini/Ross supersized books are a bit too preachy for my tastes.
As for Sandman, I'll start her off on one of the middle books (Brief Lives or something), and let her work her way around it. All she needs to know is that the Sandman is the king of dreams. Start too early, and you get the JLI and everything that this invokes: start too late, and you spoil the conclusion.
