Here is a program I found called "Just Around the Corner for Girls" and it is geared toward girls in Grades 3-5 which is right in line with your Stepdaughter. It highlights:
• When to expect the onset of puberty• The physical and emotional changes of puberty• The maturation of the female reproductive system• Menstruation• The importance of good hygiene and healthy habits
It is $69.95 brand new but you may want to search eBAY for used ones. They also have another product " Clean Kids" that you may want to look at for the same price.
Here is a site that offers tip on teaching good hygiene to boys but can be used for girls as well. I guess we assume girls already get it but this is not always the case.