Dont young fushia bloods have to kill the adult or non-heiress fushias? i know that (at least) 2 exist "peacefully" at the same time (HIC and fef) but didnt fef have to cull another fushia before the events of homestuck? if so its quite possible the hiveswap young fushia was the one she had to cull

Fef didn’t have to kill anyone. Only 2 Fuchsia bloods are alive at a time. When the young Heiress reaches adulthood she has to fit the Empress to the death.