Turns out Sakura knew Ginren is a rakshasa, she was told by one of the maids in chapter 85.
But its been a while since then, they probably could've done a better job reminding us...
Also, we've actually seen Rinxie before, it seems she's the blonde woman who caught Sakura peeping in chapter 82. That's the moment Rinxie was talking about with Ginren in this chapter. And she helped Sakura fight off the ghost in chapter 91, so she's probably been following Sakura around for a while.
