Why does lenina have second thoughts about going to the savage reservation with bernard marx?

Goes to the reservation (rather than the north post) - she needed to go to America and Mexico yet she really goes to reservation in view of medications and she doesn't think too profoundly so she simply resembles whatever she had a selective method for getting in (she loves his shoulders, kind of preferences him since he is novel, however when he begins looking at fascinating things she rejects it). She is oblivious and somewhat moronic