Hey! I read 'Have Space Suit..." for the first time when I was 18. Loved it. (and still do).

I will point out that you were never an eighteen-year-old girl, unless there's something you REALLY haven't been telling us. I read "Have Space Suit, Will Travel" during college, and enjoyed it very much.

I was thinking about something likely to appeal to somebody who isn't already thoroughly hooked on SF and Heinlein, though. I think my choices would probably work better for most older teenage young women these days.

"Harsh Mistress" hands-down favorite Heinlein, and probably better to start a 17-year-old off with than any of the juveniles, especially Poddy, as it was dated years before it was even published.

"Have Spacesuit" is also great. I was in my thirties before I discovered it, having shunned the Heinlein juveniles till then, don't know why.