I'm 75 and do not particularly look forward to Christmas because it can be exhausting cooking for lots of people and assembling everything at the end, avoiding food getting cold. At the age of 80 I would be hoping to pass the baton on to my son - and he can, and does, cook for us quite often on a Sunday but it is a much simpler affair.
Your friend has only herself to blame if she insists on making such a production of it - home made everything and all the trimmings. You have gently suggested that she might make things easier for herself by cutting some corners, but she says it is "expected" of her. So really she has only herself to blame. Her daughter and partner are being thoughtless but perhaps they think she enjoys the whole build up. Unless she tells them otherwise, things are unlikely to change. Unless you think your being more forthright on the issue will cause a rift, perhaps you should say there is no point complaining if she isn't willing to suggest they do it from now on, or at least make some adjustments so that it isn't so tiring.