I understand your rationale, but coaches need to know these things (even if it's just a very bare minimum knowledge "I have a very sick family member back home") because it affects training and mindset of the skater.
If the same situation happened to Jason Brown and Kori or something like that, then it makes sense for the skater to disclose to the coach. Mao and Rafi only worked together for 2 years. It makes sense that the relationship isn't strong enough for her to disclose "very sick family member back home"
Her mom didn't get very sick in 2008. It makes sense that she would stay in Japan to be closer to her mom and family during the hard time, and she didn't even know how long it will last.
I wonder why people insisted Mao must disclose her family problem with her coach of only 2 years.