The woman who played Isis was a former playboy bunny who a few years ago was charged with murdering her husband. I think she is in prison now.
That's Victoria Vetri, and again, it's never been confirmed that she played Isis.
This has been hashed out before. As I recall, the whole rumor started because some fan saw a pictorial of Vetri in an old issue of Playboy,
thought she looked like Isis, and noted that the timing was more or less right. He posted his theory online, other people ran with it, and pretty soon people who ought to have known better started listing Vetri as Isis in various reference sources. But it was never established by anyone who would know or whom had seen anything official.
In short, we know
how this rumor started. And we know that it was just a guess on some fan's part.
(For what it's worth, my girlfriend--who is a professional sculptor specializing in realistic likenesses--has compared Vetri's face to "Isis" and felt sure they weren't the same woman.)