Define Plastic Bitch Meaning

A bitch, hag, whore, slut, generally-bitchy-female, dressed in the most revealing, plasticly shiny clothing, and composed of no less than 86.325% make up.

Someone who is unable to be changed or adapt, is very annoying, aggressive, belligerent, unreasonable, malicious, a control freak, or rudely intrusive

Your friend is being honest to you and you were like thinking that she's lying about something, however your thoughts was false.
So you say it that she's not a backstabbing plastic bitch.