I would stay away from learning about relationships if i was you….if shes young/a teen its likely not going to really go anywhere and its just out of sheer interest and not desire to grow. I would steer away from this topic and maybe offering to learn about women in the torah? A good book would be mirrors of our lives or from sarah to sarah. If she only is interested in this then i agree learn gila manoloson.
For learning about Hashem i would learn some version of Derech Hashem. There are english versions with commentaries and stuff. They writing might seem dry but derech hashem is fasinating and really complex so do it only if shes smart.
May i ask which program this is because I heard of a similar one but they provide these basics for the pairs before the learning begins.