The Villainess' ruin is my fault, but I'll try to make her happy with the power of the curse.

Alternative

悪役令嬢の破滅の原因ですが、呪いの力で彼女を幸せにしようと思います。; Akuyaku Reijō no Hametsu no Gen'in Desu ga, Noroi no Chikara de Kanojo o Shiawaseni Shiyou to Omoimasu.