I read this novel about 30 years ago, so I needed some memory jogging from Titania and Liam before I could remember much. What I did remember unaided was the mood of the whole novel, and the friendship.
As Titania hints, while a hint of sexuality is present, our reception of such books may have been damaged by the current mondial obsession with p?dophilia and sexuality, something that probably belong to adolescence and beyond (with a few outriders, stretching back into childhood) and, in this case, lesbian relationships.
It is surely that the symbolism of the ice castle and the idea of friendship are the central parts of the novel. If we start making it a lesbian "Lolita", I think we may be barking up the wrong stalagmite.