oh then there is other route? Mine has 2 time to kill her or not.
1 is when you progress story with Tiffany and put the tracking device to the "mother" Bailey talking about, then visit Bailey in that time you'll give her a bottle have a part of the "mother", she consume it which she's mistaken for food, then the "mother" which part of her in the bottle talk to Bailey and let's she control her body and attack you, after you fix her you then have 2 option is to kill or spare. The dialogue this time is kinda sad for Bailey if you choose to kill her.
2 is like I said in the comment before.