If you watched the Portland trailer closely, you’ll realize that there are 8 individuals that have become Portland roomies. Also, Avery says she’s living in a house with 7 beautiful strangers. So what’s the deal?
It’s really no secret by now that there is a replacement in the house. IN past seasons (Cooke in Vegas for example) the trailer did not show the replacement.
There’s no definite answer that would determine why MTV has decided to reveal the eighth roommate. Logically, we can assume it’s because Nia brought a lot of drama into the house, and that was important to include in the trailer. Also, Joi was in the house for a very short period of time. It was probably too hard to edit Nia out of all the content included in the trailer.
So if you were wondering, there’s your answer.
Stop Being Polite 
Maybe Nia came later. And was just an original roommate.