It's random when Gracie appears. Some have waited months for her to arrive.
Found that it helps to get Katrina out of your event plaza if she still there. One less special visitor that week.
Make sure to buy 100K with a sold out sign for it to count for the upgrade.
If you do see Gracie you can pass the check and than change the time only to 559am. Wait for a new day and Gracie will be there. Repeat until your done. Make sure to talk to your villager each time before you change the clock back since it's a new day again.
It is completely random. She can visit anywhere from every few days to not seeing her for months on end, unfortunately. As far as I know, Gracie is one of the rarest occurring vistors in the game and she only shows up by chance, regardless of anything else you do in the game.
Well, I never saw her until I upgraded to the store before the one requiring her fashion checks. Otherwise, she shows up just like every other special visitor.