I, too, am surprised at a shelter insisting on wanting a pregnant cat to give birth there, as opposed to the current foster home . . . odd! Sounds like Mattie-Grace has the optimum environment to bring her new little lives into this world, and I hope you will be able to witness the wonder of it all. If they are FeLV+ it is not the end of the world . . . my two FeLV+ adults are otherwise healthy with no apparent problems and they are several years old now. Blessings to you and her and the little ones!