It all got out of hand. She had probably heard of other girls doing similar things to punish parents/guardians without there being a city-wide search for a corpse. It was a little naive of her. Then she was probably too embarrassed to return when she realised it had got out of hand.
It's a strange dynamic having a girl grow up with a young woman with no experience being a mother, never married, went straight from college to coaching Alina (I think she might have been still completing her education when she started coaching Alina). Alina was somewhat of her first project I'm sure there were plenty of mistakes made a long the way in raising her (like most parents/guardians) and even training her.
Alina probably finds it all a bit suffocating now as a 16 year old. Probably looks at Fedchenko and thinks I don't want to be like you at 27. Wants to get out of the situation, change training camp, but doesn't know how to go about it, doesn't know how to break it off. She's lived with her for half her life, Fedchenko probably sacrificed a lot, she would have to move back with her mother.
It is strange to live with a coach, but not as strange as parents sending their children off to dysfunctional boarding schools, having them suffer through such things as violent hazing rituals. Horrible stuff.
The coach was a little naive taking her on, or never expected her to stay for so long. No good deed goes unpunished. Lesson learned for her.