With this setup, Wyrm Prime (https://overframe.gg/build/354082/wyrm-prime/hildryn-support/), and this sentinel weapon (https://overframe.gg/build/374022/) I have been able to easily complete all content in the game without any issues.

[Boreal's Hatred] could also be replaced with [Primed Vigor], which would require another forma. [Vigilante Vigor] is also an option. Running the other 4 Vigilante mods on your sentinel gives a 20% chance to enhance a critical hit, and [Vigilante Vigor] brings that up to 25%.

With the addition of the Archon shard system, 3 Tauforged Crimson shards and 2 Crimson shards all used to buff ability power brings it over 400, which results in Pillage stripping all armor or shields in one shot, plus Elemental Ward gets a 100% stun chance. Between this and the augment [Blazing Pillage], it's a nice bit of CC. An alternative to stacking that much ability power would be to replace at least one of the Crimson shards with a Tauforged Amber shard and select improved casting speed, as all of [Hildryn]'s abilities are affected by it. With this system being new, I'm also working to see what is going to be the best setup for this as well.

If you don't have Arcane Aegis or Arcane Barrier, Arcane Nullifier or Arcane Resistance are good alternatives. Toxic damage bypassing shields is [Hildryn]'s biggest weakness due to her small health pool, and the stacking damage from magnetic procs can also be an issue.

My weapon of choice is this Bubonico setup: https://overframe.gg/build/358853/bubonico/covid-86/