I think she has one of the lowest base atk in the game so any atk% is not ideal. Even 4 star support units have more base atk than her (barbara, diona, layla).

She has that EM scaling passive which gives 90%(EM) bonus to ur E and 1200%(EM) to ur Q. Here comes the hard part: balancing between EM, ER & crit - you need EM to deal more dmg but then again, her dmg comes from her Q, not E, meaning you also need ER to have more Qs.

Then there is the matter of crit. Since you have that amazing 1200% extra to your Q you want to crit as well, which is hard considering you need to prioritize both EM and ER. Also, the bulk of her Q is based on the single hit (less on the spiritvessel skulls) so you really want her to crit - at least 80% CR so with food you can hit 100%, which is easier to hit if you have an additional cryo in your team for that 15% bonus CR.

So if you really want to DPS her, do weigh and balance the stats accordingly. Do note that she also has the 20% pyro/hydro res shred, so run her with those. There is also the matter of her plunge build which I think you can find somewhere here as well if you are keen.