Swissgemma, they may well have that kind of relationship- but if Sarah was my daughter, and she was friends with Jo, they would not be allowed in my house alone, they would not be allowed alone in my daughters bedroom, they would not be having sleepovers in the same room.
In my eyes, Jo is a boy.
The guides are enabling children to have underage sex by this policy. And not just lesbian sex (before you bring that up) which will not result in pregnancy. Pregnancy is dangerous. Childbirth is dangerous. STIs are dangerous.