From the news articles linked above... the neighbor noticed the plates were GONE on Wednesday... she didn't actually see them BEING removed.
http://www.ktnv.com/story/13707167/...es-her-own-search-for-answers?redirected=true
Her sister said that in addition to knowing that Debbie was pregnant in the fall (but not when she disappeared) that she had also known there was a "third party" involved in the situation.
This was while they were discussing the domestic abuse charges, where Debbie had supposedly gone to the new girlfriend's house and the ex/boyfriend had beaten her up there... (in the fall, while she was pregnant according to the police report.)
I believe that is what she meant. That there was another woman involved in the situation.
I don't think she intended to give the impression that it was an open relationship. It did not sound that way to me in THIS particular situation. Of course that is a possibility at some point, but in this case I think it was the "other woman" type of situation.
Whether Debbie was confronting the ex/boyfriend for cheating on her with this woman, or for hooking up with her immediately after they broke up, or if she just went over there to discuss the pregnancy and things got out of hand. I don't know. But I think it was one of those from what her sister said.