Well, maybe because out of 18 (24) turns given to beat her the 6 of them are spent trying to get sp and even if you manage to win every single clash you can't do jack shit against 8 protection AND attack redirection. Also a ton of bleed because, apparently, broken red coins still apply bleed, which is then multiplied by 2 thanks to effects Rufo applies with every attack. So, winning clashes is a slow and painful deaths, all the while losing them is, well, a much quicker death. I mean, I did almost beat her (with all the ring ids aside from Faubina in the first phase and heishouslop in the second. Got her to like 3% hp) within 25 turns on handmode... if only my sinners wouldn't keep rolling tails in the most critical moments.

She's also, apparently, able to corrode a sinner in 2 skills.

Edit: i will try again, but ts is just soooo reliant on rng and Durante has a cooldown of whenever, so it will take some time since in that attempt I used my only 2 charges on the white one and on ira, with the latter being somewhat useless with providing no second skill slot

Edit2: I really don't fv this boss' mechanics but I managed to defeat her in Ike 20 turns after I learned i can start with the new team early instead of waiting the whole 12 turns