the article was in the Times , too but better expressed.
I am an English teacher : I can tell you that task (as actually set) is a real old chestnut and has never caused me issues (I have called it her 'last letter : it emphasises the motif of letter writing in the play)
Also, because of various information sharing issues in school, it is likely that the teacher did not know her pupil's personal experiences. In fact,the whole text could be problematical there rather than only the task.
The exam board once set Education For Leisure ( a pome). They had to recall the anthologies because of a picture of a knife. Our school had permission not to teach it because of a murder.
English teaching is a bit of a mine field : so may texts confront MH issues . this year, I have had to avoid Plath at A level but have still got the potential awkwardness of Streetcar and God Of Small Things
(Disclaimer : wouldn't get class t write Plath's suicide note)