I think to abdicate would cause her so much distress that it isn't an option, certainly while she has her full faculties which obviously she has. As has been said, she is already passing a lot of her work to the younger royals and she has the sense to pull out of engagements when she really feels unwell as we have just seen. I am guessing that Charles is doing almost everything already apart from the weekly audiences with the PM, her red box and her public engagements, she must have been training him up for the job.

Mind you, if she lives as long as her mother then it is possible that she could end up burying Charles before he could become king, she could have another fifteen years in which case he would be 79 and anything could happen to him before that. This is the problem with such a young queen.