On Female, Tweens' Adolescence Literacy, Care Package Kits:

http://www.mayoclinic.org/healthy-living/tween-and-teen-health/in-depth/menstruation/art-20046004

It's important for tween girls to have:

A couple books about menstruation, periods, and adolescence, recommended by the children's librarian.

Also, they require:

A purse, pads, unscented, sensitive skin (large, witch hazel) wipes, an extra complete outfit and pad organizer, in their school locker, in case they start their period at school. There should be a discussion about how exactly to apply menstruation pads to their underwear.

Try to find a free website that discusses normal discharges, and managing cramps for tweens that you personally check for accuracy. It's important they get comfortable (sports) bras, appropriate fitting, supportive swimsuits, especially for P.E., and athletic/fitness activities.

Their skincare regime (facial cleanser, toner, facial wipes, body wash) may need changing, due to oil glands becoming more active during adolescence. Cetaphil Oily Skin Facial Cleanser, Cetaphil facial wipes are good. Acne can be caused by sensitive skin reactions to harsh acne products also. A weekly facial with Proactiv's sulfur mud mask is beneficial.

If Proactiv's products don't help, consider Image brand's 5% Salicylic Acid acne-prone mask once per week, available at some day spas/professional estheticians' shops. There are teenage facial peels you can order online for at-home use. NaturalSkincare.com has 10%, light, salicylic acid peel kits. It's best to use it only once per month, with parental/guardian's supervision, and use Image brand's physical sunblock (for oily skin) three times per day, every single day.

http://www.naturalskinshop.com/chemical-peel-center/peels-by-active-ingredient/salicylic-acid-chemical-peel.html

It may require a dermatologist (a board-certified, medical doctor specializing in skin conditions) if they have a sensitive, acne-prone skin type, or cystic acne. Sometimes, doctor-prescribed topical antibiotic gels and oral antibiotics (taken by mouth) are needed for acne treatment.

***Always try to keep the same menstruation kits, skincare facial wipes, sunblock kits for them in their home, vehicles, and in their school locker.***

***Around the eye area, sunblock can run into their eyes, causing irritation. Try to have a SPF 75 stick form of sensitive skin, micronized, invisible zinc oxide, to address that. The UPF 50+ hats with neck coverage are also excellent.***

***Unscented pads, pantiliners, shampoos, conditioners, body washes, laundry detergents, fabric softener sheets and antiperspirants/deodorants are better, to prevent skin rashes, and bug bites, as added fragrances attracts biting insects.***