What if Her Majesty Queen Elizabeth II was to trip along the cobblestones on her way into worship at the church?

Rest assured, One would make sure One didn't slip. In other words if she was feeling shaky, she'd not be there. And if you've noticed, HM always wears shoes suitable for the occasion.

Taharrush by Cologne Cathedral

The material world is full of danger at every step. Only solution is to to take Shelter of GOD. Krishna, Jehova, Allah are different names of the SAME GOD. There is only ONE GOD. Devote yourself to His satisfaction and GET OUT of this dangerous material world.

Given her age she could get hurt

Superman would save her from injury.

People would help her, and make sure that she was not injured.

And............

It would be the most played clip on YOUTUBE for years. Most of the hits would be from Prince Charles.

I expect someone would help her up and ask her if she is ok, the same as they would with anyone.

Her ladies-in-waiting would scoop her up and smooth out her frock, get her hat set back squarely on her head, pull up her stockings if they had come loose from their thigh garters, place her shoe back on if it had come off, and brush any debris off that may have attached itself to Her Majesty. And if her wig were askew, they would discreetly move it back into proper alignment. Her handbag would likely not have fallen off her arm as Her Majesty is known to always keep it securely in place. If Her Majesty was injured, the ladies-in-waiting would carry Her Majesty to the nearest room and lay her out on a table whilst calling the royal physician.