To be honest, this is disappointing to hear.
I would expect, that the majority of switched on crew, would offer a hot drink to your Mum after being asked a question like that.
It really is sad to read that this crew member was not responsive to her needs.
It really is part of the service for crew to look after passengers and serve them at their seats, part of the SCCMs introduction actually invites passengers to use the call bell or visit the galley for any drinks. Personally I find it is strange that any crew member being asked that question would have not immediately realised that this customer wanted a hot drink!