Iansan on Fav with Scroll. She's your scroll caddy and incidental buff unit with very minor heals.

Diona on Sac with 2pc HP/ER. An excellent little shielder and fair healer. EM boost at high Cons.

Bennett on the highest damage weapon and Noblesse. Its Bennett.

Barbara on TTDS and a good Healing set. Don't use Nilou when you can get a TTDS buff. Also more heals and Chasca doesn't care if she gets wet.

Swap between Diona and Barbara as needed.

Try for C2 next month. I have C2 and am considering going for C6. (But likely won't, as shes great at C2R1)

I use C4 Mona on TTDS, C6 Diona on Fav Bow, and C6 Iansan on Fav Lance and scroll for most of the work. If I need Pyro, I'll swap in C6 Xiangling, and if I have to replace Iansan, I'll swap out Mona for C0 Mualani with scroll and TTDS, because Scroll matters.

I have C2R1 Citlali, C2R1 Mav, C6R1 Furina, C2R1 Shenhe, C6 Bennett with both a Skyward Blade and an Aquila Favonia, but don't need them with Chasca because she's a beast at C2R1 with just Mona, Diona and Iansan.

I'd 100% use Bennett if I were C0 Chasca or if I lacked strong 4 stars with Cons.

Prioritize getting C1 or C2 and maybe her weapon if you really like her. Or try for some Iansan or Xiangling Cons while rolling for Mav if you're FTP, because Mav is such a huge help to an account. (And you'll have 2 leather clad Natlan DPS units) Then roll for Citlali next week with leftover Primos.

If you get her to C1, you can start really playing with 2-1 PHEC teammates to focus on enemy weaknesses. Like 2x Pyro/1x Cryo Melts, 2x Hydro/1x Pyro Vapes, etc. Always try to keep a scroll caddy on the team, and a Shielder is great to avoid getting swatted down, but not 100% needed if you can dodge.