Is "little" code for "innocent"?
Given the evangelical background of the author, this isn't too surprising. The eternally infantiled woman is the ideal, in that headspace.
It would be one thing if this was about really young girls, but it's about teenagers, for crying out loud.
"Little" = "non-sexual." That's really all it comes down to.
Maybe the mom who wrote this book just thinks that the ideal romantic relationship model is a Daddy/little relationship, so she's trying to prepare her daughter appropriately.
Jiminy Cricket! I must say this possibility had never occurred to me. Never ever.
That's actually a little less offensive than the conservative/traditional infantilised woman thing. Assuming they end up engaging in consensual Daddy/little relationships.