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She kept saying she was a college student, but no matter how I tried, I just couldn't bring myself to believe it.
Literal
She [topic-は] many-times self [topic-は] college-student is [quotative-と] said [but-が] I [topic-は] no-matter-how that [object-を] believe mood [contrastive-には] could-not-become.
A long sentence packed with useful pieces. The first half repeats the same self-defense frame ('she kept saying ~'). The second half hinges on どうしても + 信じる気にはなれなかった — a slightly elaborate way to say 'no matter how I tried, I just couldn't get myself to believe it.' ~気になる literally means 'become in the mood/inclined to,' and ~気にはなれない/なれなかった is its negative-with-contrastive-は form: 'cannot bring oneself to (do).' Adding どうしても strengthens the impossibility: 'no matter what.' The whole construction is an idiomatic way of conveying genuine inability, not just unwillingness.