。
She wouldn't change her mind, no matter what.
Literal
She [topic-は] no-matter-what resolve [object-を] change [(emphatic) try to-ようとは] did-not.
決心 (kesshin, 'firm resolve, determination') is heftier than 決定 ('decision') or 思い ('thought') — it implies a settled, deliberate inner commitment. The は inserted into ようとはしなかった (instead of plain ようとしなかった) is the contrastive/topic は, sharpening the negation: 'as for trying to change, no — that didn't happen.' The pattern Vようとは＋しない/しなかった is a stock way to add emphatic flavor to the refusal frame, drilling home that no attempt was even made.