My daughter has just turned 12 and was in 6th grade.
The elementary school nurse had a special session with all the girls in the 4th grade for informational purposes so they would be somewhat prepared because some moms just don't prepare their girls for it.
I believe in wide open communication lines with no topics off limits. It's the way I've been with my now 17 yr old daughter from day 1. COMMUNICATE. Answer questions, talk about whatever she wants.
Some moms are prudes (MINE) and was so much so that she made the woman's body sound like it was dirty and extended those opinions to sex. That is SO WRONG. Once she was in the hospital and I saw her vagina and she was SO embarrassed. I was at least 14 and i said... Gees... every female has one, get a grip, yours is not all that! Things were slightly better after that.
Starting in 6th grade, my daughter had a little cosmetic bag with a couple of pads if needed. The school nurse also has supplies for emergencies.
In the beginning, my daughter was perfectly regular. About a year ago, she started bleeding non stop and we ended up on a very light dose hormone to control her cycle. That has helped a lot.
Your daughter might wear pads the first month and at night but don't be alarmed when she asks for tampons. It is OK to let her wear tampons, just explain the importance of changing in a timely manner. They make slender sizes for younger girls.
Relax and get ready for some mood swings. I helped my daughter chart her cycle up until she went on the hormone.
Just stay open with your daughter and talk a lot. You'll need those communication lines wide open at 17!
Good luck