I think if she Able to track and walk you can make sure she is fine and good hearth before reach kedaranath , and I thought don't let her to long journey and cold places it's not good for health regarding her age thanks
Yes age isn't an issue. but if you go through certified trekkers like Indiahikes, there are a few body tests that a person has to pass to be able to go for a Trek. so if she clears that then it's good to go!