She made her „train to death“ because someone made a negative comment online. Putting it very lightly, she might not handle any criticism well. I’m waiting for another part of the article to be translated and praying it was a mistranslation and sounds different in Chinese. :-/
Regarding mistranslation, I think the errors are minor (e.g. the phrase you mentioned, 死劲, is more like 'vigorously/doggedly') but the main gist of heavy training and harshness is accurate. Google Translate tends to cope worse with direct quotes from Ms Zhang, since she uses many colloquialisms and cultural/historical references.
As a general remark, the focus of this article isn't really about Nini's (honestly slim) Olympic prospects - it's more like a human interest article, hence the meandering length. I'd be interested if anybody here with a psychology background could analyse Ms Zhang. Pre-emptively reading counselling material for bereaved parents is uniquely weird compared to, say, Tonya's mum.
I agree that the interviewer is milking the drama quite a bit for entertainment value. Scenes described by Ms Zhang and observed by the interviewer are both rephrased like a narrative, blurring the distinction between first- and second-hand information, but plenty of verbatim stuff is quite disturbing, unless the mother is being very hyperbolic/sarcastic.
Still puzzled as to why Ms Zhang would consent to this interview/feature in which she suddenly does an about-face compared to her previous media features... it's hardly beneficial to her. In China, society may be more accepting of harsh training than in some other countries, but only if it's proven to be effective and if administered lucidly by professional coaches in a sports school environment, which is very much not the case here.