I found an article that gives information about it : Uli John Roth says Virgin Killer album cover makes him cringe ; archive, but the link to the original interview they give doesn't work.

It says :

Classic Rock Revisited: "Virgin Killer" was banned!! Who was the girl on the cover and whose idea was it to have a nude child with broken glass in that area? What a statement.

Uli: "Looking at that picture today makes me cringe. It was done in the worst possible taste. Back then I was too immature to see that. Shame on me — I should have done everything in my power to stop it. The record company came up with the idea, I think. The lyrics incidentally were a take-off on KISS, whom we had just supported on a tour. I was fooling around and played the riff of the song in the rehearsal room and spontaneously improvised ''cause he's a virgin killer!' trying to do a more or less way-off-the-mark Paul Stanley impersonation. Klaus immediately said 'that's great! You should do something with it.' Then I had the unenviable task of constructing a meaningful set of lyrics around the title, which I actually managed to do to some degree. But the song has a totally different meaning from what people would assume at first. Virgin Killer is none other than the demon of our time, the less compassionate side of the societies we live in today — brutally trampling upon the heart and soul of innocence.

"I can't blame Tipper Gore for brandishing the cover on TV as offensive, though. She was completely right in doing so and she's a good person anyway, although she probably didn't make the effort to check out the lyrics, which put a different slant on the whole thing — can't blame her for that either, because knowing what I know today, I would have possibly reacted in a similar vein. Incidentally, I read Al Gore's book — 'Earth in the Balance' — and I can only wholeheartedly recommend it to anyone who loves this planet of ours. His vision is strong, clear and inspired there. Shame not enough people got to read it."

I feel like he's lying and painting an innocent picture of himself. But he's trying way too hard. (My translation : "I can't even look at it, I was too immature, shame on me, I should've, it's not my idea, I created the lyrics by accident, I didn't want to construct the lyrics, it doesn't mean what people think it means, but I agree it's offensive and that woman is a good person even though she didn't read the lyrics the stupid f*ck, hum let's change the subject, I've read an interesting book, blablabla.")

Also, he never says who was the girl on the cover.