Not A Main Nor A Fishcl User At All。However、Here Is Roughly What You Want From/For Her。

Assuming You Aren't Building PHYS DMG、We'll Gloss Over Her。Her Build Really Depends On Usage Situation、Let's Just Go With SubーDPS。Even If You Aren't and Are Playing Her For Elemental Advantage I'd Say Use The Same Build With Some Energy Tweaks。

Golden Troupe (Fontaine) Is Her BIS For Artifacts。
２−PC: Elemental Skill Dmg Increase (20%)　＋　4ーPC: Boosts By 25% (Concurrent With 2PC Buff) and Is Further Increased by 25% When Off-Field。

Gilded Dreams (Sumeru)、Thundering Fury (Mondstat) & Gladiator Are The Other Contenders If You Don't Have GT Domain。Gilded Dreams Is A Great Substitute For SubDPS。

Now For Actual Stats:

What You Want To Achieve Is A Focus On Elemental Damage Rather Than Anything Else。
Atk% or Elemental Mastery On Your Sands。
Electro Dmg or ER% On Your Goblet。
CR/CD Criclet。
　「 EM Doesn't Crit、So If You Want To Use Her For Reactions、Do Not Use A CD/CR Circlet! 」

Fischl Rely's Heavily On Basics And Elemental Skill Damage。Her BIS Weapon Is: Polar Star。Obviously。　It's A Crit% Sub 5*。Other、Easier To Attain、Options Include But Aren't Limited To:
- The Stingless (BIS 4*、165 Elemental Mast. @ lvl90。 Also E & Q Dmg Boost。)
- Skyward Harp (Not Optimal。 Provides Minimal CD/CR and Nothing Else。)

There Is A Myriad Of Other Weapons She Works Well With、However、Most Are Geared Toward Her Phys SubーDPS Kit。Regardless、Good Luck In Building Her。