The male member of staff crossed into the bra dept and approached the teenager while the mother was standing apart from her and hidden from view. This is directly from the mother. Ie. That member of staff did not know the teenager was shopping with her mother when he approached the teenager.
She confirmed that M&S informed her by letter that the male member of staff was allocated to be upstairs and not anywhere near the bra dept.
And again, what part of asking if someone wants help in the bra dept would not have the expectation that that ‘help’ would entail discussions about size, style and usage. None of those are appropriate for a male staff member to be asking a teenaged girl. Even when with their mother there.
And your constant denial of ‘but they don’t know whether the person was trans or not’ misses the entire point. The point is that it was a male member of staff as identified by the mother and the daughter. If you, personally, lack the ability to identify the correct sex of a person through observation and interaction, please stop believing that this is the norm. It is highly likely that a female person will correctly identify the sex of a male person with observation and interaction.
You seem over confident in your very own interpretation of the facts and determined to excuse the harm caused to this girl. Why?