東方玄夢妖譚 ~ The Nightmare of Rebellion - 嫩蝶牡丹 推参!
0She is weak against Lightning and Slash with a high Magic Defense so don't bother going for magic (like you saw on Marisa) and go offensive!
At start, everyone is Poisoned (unless you paid attention on the cutscene) so it can take 2-3 turns to dispose them but if Saya's LW opens up, use that instead. Then have everyone go buff to start dealing damage on the next turn.
Chasers are seriously a must in this fight! Luckily I assigned one to Yukari (cuz Lightning+Slash weapon) while the other on Reimu (I got nothing :V). I bothered to try using Yuugi at that time to see how it deals and unexpectedly, WOW! That somehow saved me time and had no problems taking down the boss without having her LW triggered. Oopsie daisy~ *sarcasms*
I was planning to use Fairy Maid's Control Land on Turn 4 but when I saw the damage and killed her, eh nevermind! What's done is done!
With the second seal open, only one remains! Godspeed, girls!