According to the ironically-named CineMorgue.com,
she was indeed 40. IMDB is infamous for intentionally downsizing certain female actresses' ages, and refusing to change them no matter how many times you submit a correction. I can only guess that if you're willing to pay for IMDBPro, you get to control what goes into your listing.
I just punched in death data for Lana Clarkson at IMDB. Let's see if they bother to accept it.