Is this a sign of childhood sexual abuse or some other mental affliction?

What could be possible explanations/diagnosis for this?

There is someone important to me, a woman of around 38-39 years old that displays promiscuous behavior, and has been for as long as I can remember (since at least 18 years old, but could be longer, don't know). She puts up suggestive pictures on the internet, sends dirty pics via e-mail & phone, and seems to be addicted to men's attention.

I recently found out something that leads me to believe it is more complex than just simply being promiscuous. Once when her daughter was a baby, a man that was having intimate relations with her saw her writing in a notebook one night. He managed to get a hold of it, & discovered she was keeping a log of all the men she had sex with that week. When the man confronted her about a certain individual on the list (it was a friend of his) she denied it, and swore on her baby daughter's life that she did not. He then pulled out the notebook & she was speechless. Documenting things like this seems to indicate a mental problem.

Also note, she is very secretive about these kinds of affairs, she puts off an image that she is a simple woman raising her kids that does not have a social life at all. She always says how she is "so nice". She would sware up and down (and on her children apparently) that she would never do such a thing.

Another note, she is not unnattractive, at least with the general consensus. I've never heard/seen anyone who didn't think she was pretty/hot/sexy/etc.