Ellen probably wouldn't have survived, let alone broken the record, if she didn't have such extreme mental toughness.
Is it the third conditional? I guess, they talking about past events that didn't happen. Then why "if part" of the sentence contains the past simple verb and not the past perfect?
Also this sentence from the same text
But if she hadn't endured such tough experiences herself, she wouldn't understand nearly as much about what these young people have to face.