I’ve been thinking about everything that happened in the finale and some things have become apparent to me. This is how I think everything panned out with Audrey helping Piper.
-Audrey was the one that stole the mask in that flashback. She was burning the documents that were with the mask and that was why her DNA was on the mask. That also means she’s been ‘recruited’ by Piper for a while (as she got her to steal the mask).
-Audrey wanted to help Piper because she said she was going to kill Nina, a person who has been torturing Audrey for years. But then, she killed Rachael without Audrey’s permission, and Audrey didn’t want to help her anymore. But Piper had proof that Audrey had been helping her, so then she started blackmailing Audrey into helping her.
-This would also explain why there were survivors - when Audrey was wearing the mask, she didn’t have the power to kill. She didn’t want to kill, nor did she want to help Piper. This is why probably why Jake survived.
-I think that Audrey was the one who tied Seth up and took him to the car for Piper. That’s why Piper attacked her at the party - so she would do the deed for her. Piper was busy attacking Brooke, so needed Audrey to get Mr Branson. That also explains why Audrey went missing at the party for so long.
I don’t think Audrey is a bad person. She was a misguided person that had the threat of death hanging over her if she put a foot out of line.