Ditha can make a biggest life gap but has more weak points. While Louise is only seriously affected by SoAs (and 6 power is still playable), Ditha is affected by SoAs and DRs.
And if Louise has her 9 power active I find it more decisive.
When i played with Pussycats,i tried them both,I perferd Lousie
I would lean towards Ditha. (Though I haven't tried Louise)
My highest ELO score is from using Ditha in mono Pussycats during a week where Roots/GHEIST were unpopular. Her potential for a 14 life gap when all your other cards damage reduce is really good. I often sink all 12 pill into her.
I would use Ditha she isn't stopped by soa because she would still be a 7,5
Louise costs more for a reason
"Louise costs more for a reason"
This isn't always a good indicator.
XU52 costs 3 times more than Rolph and isn't anywhere near as good a card.
Selma is half the cost of dalhia, but they're pretty much balanced.
I think both Louise and Ditha are equally great. All depends if you prefer attack power or gap potential.