L!Erika Iv

Fodder the -def +res one and keep the -atk +spd one.

You've been at this game more than 3 months. I think it would be good for you to try this question out yourself because the answer isn't easy or obvious. We can provide some tips but you will probably need to experiment a little.

I'll give you pointers on each of her stats:
Atk: is slightly on the low end, but her weapon hits extremely hard and atk/spd solo grants a lot of atk, and hone cavalry is very strong. Plus, lunar brace lets her hit extremely hard with her special, so -atk is definitely an option despite not being preferable.
Spd: 39 is extremely fast, and atk/spd solo grants +6. If you add hone cavalry, which is a good idea on -atk and just in general, it's probably excessive.
Def: a sensitive point. She has the potential to take multiple hits to her def if she has the right build and support, maybe a fortify cavalry and/or close def or atk smoke seals. Most people probably won't enjoy her as a fragile unit, because desperation would mean giving up lunar brace (which honestly isn't bad because her weapon already hits so hard) and using lower cooldown specials.
Res: with a boon, she does get into territory where stuff like fortify cavalry and close def can combine with her weapon effect to let her take multiple hits on her res.

Being able to take two hits can mean being able to take three or four or five hits because of healing specials combining with lunar brace or perhaps even working without it because she can hit hard enough without it.