And
Hi, pleased to meet you! I am Furudo Erika, the detective!! I may be an uninvited guest, but please, welcome me!! I am the visitor, the 18th human on Rokkenjima!!
Even if you do join us-- There are 17 people.
She proclaims herself, in red, that she is the eighteenth person on Rokkenjima. Yet in the very next reply, there are only 17 people on Rokkenjima, INCLUDING her. Her Red Truth was a lie, or only a truth from Furudo Erika's perspective.