Ah, you see. That is the perennial trick of the vampire. There is no afterlife to snare their soul, no damnation or salvation - barring a few exceptional circumstances, nothing to hold them back once redead from resuming their endless existence if they can just get more life energy. The purpose of scattering the vampire's ashes as far as one humanly can isn't some punishment; it's to raise how much life force would be needed to resurrect them from ashes to prohibitive levels. With an intact corpse, as little as a single life can be required; if you just have a fingernail's worth of ash, that's... pretty damn costly.
Their soul is stagnant, withered, and oh so very hungry. The difference between a vampire who has gone too long without feeding and a vampire whose head has been cut off is non-existent; all they need is more lifeforce to resume their unlife.
So... cut off Cattleya's head, stake her, burn her, and as long as Louise can get all her remains she'll only need to put at most a few horses's worth of life force into her to bring her back. Admittedly, she'll be somewhat crazier from the time spent dead - one of the reasons vampires tend towards the 'hilariously insane' - and more withered and dead-looking in appearance [1], but the latter will fade with time and consumed lives.
[1] Hence why vampires who aren't too good at staying alive tend towards the nosferatu or the 'rotting corpse' in appearance.