Any sort of time you contract someone for work and they don’t perform the job as agreed

What WAS the job agreed?

From what OP wrote the agreement was "babysit 3h".

When the sitter arrived OP gave her an additional list and left.

If OP had told the sitter her list of demands when the price was set, I would be on your page for bad performance. But adding it after the deal was sealed and than not paying because of "errors" at this (unpaid) extras is not OK.

This is like hiring someone to paint your fence and when he arrives tell him to cut the grass too. And then you do not pay him for painting your fence coz he did not cut the grass (because your lawnmower didn't start)?