God, the Nase Family character growth arc of the entire series is so goddamn good.
There seems to be some conflicting message in this chapter, Creek's trainer was regretting that she kept pushing Creek without realizing she was injured/burnt out because she was too blinded by her dreams, and then she got angry due to her inferiority complex to her father, so she's going to keep pushing Super Creek to achieve her goal of surpassing her father.
It's a convergence of a number of factors; humans do be containing multitudes. She's already extremely emotionally charged by Creek's hospitalization, because of (a) her previous euphoria of getting really amped up for her own dreams, (b) her guilt over not noticing Creek's condition until it was possibly too late, and (c) her concern for Creek needing to be hospitalized. With that setup, lashing out at her dad the way she did may have partially been because of her inferiority complex toward him, but it was more because, if she had accepted what he said, that would have meant it really was well and truly
over, and she's not prepared to give up on either Creek or herself. I imagine he said what he said specifically to get that reaction from her, and would have been disappointed if she instead resigned herself to giving up.