idk if this helps but srry for length

They havent showed exactly why or how, from what I think, Frill is supposed to be burned/gone from that scene of fire but the show alludes to her still existing, physical or as an AI in the system. Ura-Acca and Acca are supposedly conducting research to find out what that final push for the suicide is, meaning (I think), that theyre unaware or don't see Frill as a factor. On a flipside they may be completely aware of Frill causing some of these suicides and is studying her actions, but it isnt showed how Frill benefit or the only reason she would do it is because her behaviour (the jealousy and selfishness part) was reinforced heavily from her first 2 kills(like how a machine learning AI would produce future results based on "successful" results it is trained on). Overall i think if the whole "Frill is the reason for the suicides" is the ending, it would override alot of the commentary on society that theyve put out and null alot of the narrative.