That is a brand new character. It's also going to be a lot harder to make those "perfect" fan versions of this manga when it's doing a lot more than the original pornographic version did.
Technically not a new character, she just has such an extremely short cameo in the original that she doesn't register. You'll see the connection in the next chapter. It may be a problem, though, as the author's preview for the next volume has her as the main focus...so there might be four volumes in total, instead of three...and at that rate, she might just end up joining? We shall see.
Edit: On second look as I'm translating the next chapter, it appears she actually is a totally new character. Oh, no. Not good.