SOLVED. Young girl Coming of age, get transported back in time to prehistoric days [s]

[Alicia]

This may sound weird, but I swear it was a real book. I read this book in Junior High/High School I believe (20-30 years ago!). The main character is a young girl, about 12 or 13. She had a diary in which she laments that her body is not developing (not getting her period/breasts/etc.) Her brother finds the diary and starts teasing her about it, so she runs out of the house and somehow (in a storm maybe?) get transported back to prehistoric time. She ends up living in a cave with a group of other people.

During the course of the story, the young girl she befriends gets her "blood" and moves to the "adult" cave, leaving her on her own. A pocket knife that she had, which made the journey with her is used to kill someone and she has to run away from them all again.

I cannot for the life of me remember the title!

Help?

[Alicia]

I know it isn't 11,000 Years Lost. The book I am trying to remember is chock full of coming of age angst, like a Judy Bloom novel...

[Pamela]

Saturday the Twelfth of October by Norma Fox Mazer, I think. Saturday, the Twelfth of October

[Alicia]

Yes! Thank you! That's it!!!

[Pamela]

You're welcome.