I have heard of that woman but I disagree that it was a pregnant woman for one main reason: the disguise. The disguise was completely over the top but also incredibly effective at protecting the identity of the killer. If we believe that they were savvy enough to think of a disguise that effective, but pregnant enough to appear pregnant in that disguise, then surely they would also have the foresight to not kill Missy.
The risk of them giving birth, if in fact they were far along enough to make a dent in SWAT gear, would be incredibly high and the stress from them committing an act of murder could arguably induce labour. I unfortunately don’t see a scenario where a pregnant woman drives to the church at 3:50AM and has the time and energy to kill Missy and then sneak out undetected by security cameras.
I’ll try and find the name for you at any rate.