WHOA MASSIVE SPOILERS!!
At the very end of episode 5, after confessing her lies, Nerissa turns to Bigby and says:
You're not as bad as everyone says you are.
This triggers the realization in Bigby that he's heard this before. After saving Faith from the Woodsman at the start of episode one, she leaves him with:
Hey. I need to tell you something. You're not as bad as everyone says you are.
This seems to imply that the person who appears to be Faith in the scene from episode 1 and the person who appears to be Nerissa at the end of episode 5 are the same person.
There's several potential interpretations of this.
Both women were actually Nerissa. One is that at the beginning of episode 1, Nerissa glamored herself to look like Faith so that she could meet Bigby and get him "engaged" in protecting Faith (by picking a fight with Bigby's mortal enemy the Woodsman) before leaving Faith's head at the Woodlands. Nerissa already admitted to lying throughout this process, so the revelation could be that her confession here wasn't the whole story.
Both women were actually Faith. Another is that the body from episode 1 was actually Nerissa, glamored to look like Faith, and Bigby is actually speaking to Faith both times. Bigby recalls talking about Faith's body and that Swineheart never really got back to him about it, and that more tests needed to be run. This could indicate that there was some anomaly with the body that he couldn't explain. For instance, he may have expected to find Nerissa's mermaid body but found Faith's instead.
Both women were Vivian? Still another interesting tidbit is that the woman at the end of episode 5 (Nerissa? Faith?) reacts strongly and refuses to have her ribbon removed. It could just be a natural aversion to the ribbon's removal after resisting so long, or it could be an indication that removal would kill her. It's possible that the girl at the end is actually Vivian, and that the woman who committed suicide at the Puddin n' Pie either faked it or was someone else in disguise.
We don't know who this person is. Finally, since glamours appear to disguise anyone as anyone else (ie, a troll as a slender human female) it's possible that we don't know who this person is at all. "Her" whole arc through the series may have been faked, for whatever reason.