I have to admit that I'm susceptible to the "2 Sr. Lucy's" argument. Anyway you slice it and dice it, those women just don't look the same. Certain changes happen in a person's face over time, such as the skin sagging and the nose becoming more downturned as the cartilage sags, but others don't.
The eyes, chin, mouth, and head shape of the two women are just simply not the same.
If those two women are not the same, that means that high-ups in the Vatican covered up the real Sr. Lucy's death and hid that fact from the world for four decades. Even more sinisterly, they may have even had her murdered.
If she was murdered in order for the Vatican II shenaniganery to go through more unimpeded, and the Popes knew about this and have participated in the cover up...no other proof would be needed for me. All theological arguments would be out the window. Game over. Sedevacantism wins.