Barnhardt's argument (she's Bennyvacantist) is that Ratzinger would have to be visibly present.
I don't get why people insert these extra requirements? Our Lady never said where anyone had to be, or not be, whether sitting or standing, whether at a certain time, on a certain day, neither raining or sunshine. She simply asked for the consecration, in union with the bishops. She never said everyone had to be in the same room, or city, or even country (which, is obviously not feasible, because even an ecuмenical council never has 100% attendance due to old age, sickness, etc).