Which Bowcina?

I'd personally go for -Atk simply because her speed can be fairly important, and while she gains an additional 4 to her stats on initiation against melee units, lowering it can cause problems in terms of doubling and, if you're going for it, Desperation.

What build were you planning on giving her? That might better help in determining which you should go for.

Ouch... You have my sympathies. I have a Bowcina, too, and she's also -ATK. But +SPD still lets me use her in Aether Raids. I just throw Flashing Blade 3 sacred seal on her and watch her proc Moonbows all day lol.

Personally, I'd go for the -ATK +RES one. Even though her ATK only reaches 45, she still has 38 neutral speed, which is important for her to keep. If you end up merging her, she'll get +1 to HP and SPD, bringing her to 37 and 39, respectively. Running Swift Sparrow brings her ATK and SPD to 49 and 42 (49 and 43 after merge) on initiation. That's even before factoring in Thogn's effect of +4 on all stats during initiation on a sword, lance, axe, or dragonstone unit.

It's worth noting that HP is a superboon, but that won't change her arena scoring bin. Interesting idea with Atk/Def Link 3 synergizing with her Future Vision... Not sure if I'd fodder Laevatein for a subpar IV Bowcina if I only had one, though it's a neat idea for sure.

Question: are you keeping her PRF, or will you give her a different bow?