After a lot of grinding i finally have 3 water element essence. I have untouchable peacock, silent kill valentine, cold stones beowulf and no egrets parasol maxed out. Which one should I make diamond!?
I'd go Silent Kill too. On offense, her SA can deal with many annoying catalysts. As a natural gold Valentine she's also good on defense. There isn't a lot of fighters that are good at both.
I'd stay away from Cold Stones and No Egrets for quite a while as far as evolving to diamond goes. You'll get more bang from a natural gold, unless really amazing SA (Doublicious and some others).
I'm getting close to that point as well with similar options, got advises from people on Discord and gave it lots of thoughts myself. And even though my Silent Kill needs a lot of work, looks like I'll end up saving the essences and fodders for her anyway.
Silent Kill, when you will get other 3 water essences you should go for Brain Freeze and then Cold Stones (that I still prefer to Beowulf) and Untouchable if in the meantime you still haven't got Ultraviolent or Freeze Frame.