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.
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.
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