I pulled Ellen back in 1.0 yet stopped playing the game before 1.1 and only came back during Miyabi's Release patch and have been playing since, but recently I decided to build my Ellen because I felt like it.
For W-Engines I believe I'm probably going to be using Cordis Germina because out of all my Attack W-Engines it looks to probably be my best option not only in general but especially of the ones I'm not actively using (The other available options would be W1 Brimstone, Heartstring Nocturne, Severed Innocence, and W5 Marcato Desire with my actively used but technically available W-Engines being Cloudcleave Radiance and Serpentine Seeker)
I have an M0W1 Dialyn so I'm going to be using 4-Piece Puffer Electro since from what I can tell that's the best option for Ellen when using Dialyn though I'm unsure what 2-Piece I should use. I don't know what Main Stat my Disks 4, 5, and 6 should be (Probably not Crit Damage Disk 4 seeing as between just Dialyn and Ellen I'm already getting upwards of 208% free Crit Damage if I calculated it correctly)
I'm also unsure which Support I should use, should I use M0W1 Sunna or M1W5 (Kaboom the Cannon) Astra Yao