She did only know after reaching their home. WLY decided on her own to exchange it. As usual she made WJY believe that it's WZ fault for her to end up like this.
She has always been jealous of her dad's love for her sister. So, she exchanged her dad's memories of WJY for WJY to revive her youthfulness. Their dad now thinks that WJY died along with his wife.
Not only the FL's identity, but ML's identity is revealed as well. But they didn't show the reaction of all the…
WZ was already told that YY was an immortal earlier by himself. Also YY did suspect WZ of being the phoenix from beginning though when he checked her it didn't seem so. He was not sure of WLY being the phoenix from the beginning. So, I guess they weren't surprised much.