We do have a mom friend that was so worried about her daughters reaction to having a period, the girl is kind of a drama queen about blood and "yucky stuff'.. but I remember she said her daughter handled it well and actually acted a little more mature once it all started..
Our daughters best friend is a nervous child who tend s to do a lot of shrieking and eye rolling with personal discussions and what she considers yucky topics, but even she handled it well.. Her mother presented it to her more in a scientific biologic way.. The girl did end up with horrible cramps and eventually they had to have her on a very dosage birth control pill.
I cannot think of one person I have ever known that freaked out about it..
I thought in 3rd grade they spoke with the girls about this? If not, be sure to either have a book to guide you or make some notes.. She may already know.. Let her know she is allowed to speak with you about anything at any time.. To not be shy. These are things all women go through everywhere.
Use correct language Menstrual cycle, Vagina, Urethra, Anus, then tell her the other words people use, Period,The curse , Aunt Flo, Va jay jay, butt hole, pee hole.. so she will know what to answer to a doctor or nurse, but then how to also respond if a young friend speaks with her about it..
There is nothing worse than a child having to act like they know what people are speaking about, with no clue.. Better her mom tell her..
Also show her the actual pads, and different tampons. explain how they will work. Let her know how to document the times of the month on a calendar, so it will give her a heads up on when to expect. it.. also at the doctors office many times, they will also want this information.
Also remind her to never flush any of the pads, wrappers or any part of the tampon holders or tampons.. They will ruin the plumbing (remind her she will not want to be responsible for the backed up toilet at home or in public) and back up water treatment plants.. Decide how you all will dispose of them at home and how to do it in public restrooms..
Congratulate her on being a young woman. Tell her there is nothing to worry about, but be honest about how sometimes, it does feel like a bit of a hassle, or can make you feel a little crampy, but there are solutions for all of this..