Then, when you're 25, your daddy dies aged only 56 and after a rather brief period of mourning you get pushed into taking his job in a pompous ceremony. Now you're going to be doing this until you die. No retirement! I bet there were times where Lilibet just wanted to go to her room and cry.
I wouldn't have wanted her job for all the wealth and power that came with it.
[1] Well, you could make a big scandal about marrying an American divorcee, but that didn't go down too well for the last guy.
If she had wanted to, at some point, abdicate in favour of Charles, that could have been arranged. It would have required a special Act of the UK Parliament (following the prior example of His Majesty's Declaration of Abdication Act 1936) [0] – and probably also supporting legislation in the other Commonwealth Realms (Australia, Canada, New Zealand, etc) – but no doubt the governments of the Commonwealth Realms would have obliged. It was her own decision that she did not want that. I would not be surprised if, in another 10 or 15 years, King Charles III makes a different decision, but we shall see. In recent years, monarchs abdicating due to advanced age has become rather common – the Netherlands, Belgium, Spain, Luxembourg, Japan, among others.
[0] http://www.bailii.org/uk/legis/num_act/1936/ukpga_19360003_e...
The damage in both cases were mainly to their pride. If that was all she risked, I'm not impressed. Her uncle Edward was a literal Nazi, and yet even he was willing to give up power to marry the woman he loved.
But it could of course be that she risked more than that. What keeps elderly rulers clinging to power is often the knowledge that they and their close ones has done some very bad things, and that the descent may not be so graceful if they let go willingly.