It is not advisable for your mum to visit those site at her age because the sites are all challenging, slippery and takes a lot of walking and climbing. There is cablecar on Dragon Snow Mountain and it is very cold there.

I've just returned from Yunnan (first 2weeks in December). Whether your mum is up to lots of walking at her age is her decision but I would advise against the more strenuous. There is plenty to see in Dali and Lijiang but remember that they are both at a high altitude and this may make activity more difficult. I was running up and down the hill that the pagoda sits on in Lijiang and got a headache from the altitude. The weather on Jade Dragon Snow mountain was not as cold as I expected because the sun was out and it was quite strong. I have been advised that if there is any cloud then not to bother with the mountain as it will be cold and you won't see anything.

Another point is that all the restaurants/cafes in Lijiang are unheated so it can be quite cold in them during the winter.

Also when I was there the road was closed to the main part of Tiger Leaping gorge - anyone know if it's open again?

Not advisable, i just came back. The weather is too dry and the journey is too tired for her.