Things have changed since FastPass. You don't want to tell the CM's you want to child-swap, b/c on most of the bigger rides these days, non-riders who are swapping are *not* allowed to go through the ride-line. She would end up having to wait for you in a gift shop or arcade, possibly for quite a while. (I once waited with the baby for 45 minutes for DH when he was riding Space Mtn. on a FP.) She's probably plenty big enough to ride if she wanted to, so "swapping" is not necessary.
What you want is usually known as a "chicken-exit" rather than an escape route. On pretty much all rides, you can chicken out anytime before you actually get into a vehicle, but once you sit in a car or boat, you're stuck for the duration. Presuming that you don't want to just let her tour on her own and set a meeting time, the best way to handle it is for her to go through the line with you. When you reach the loading area and the CM asks how many are in your party, she can tell the CM that she has changed her mind about riding. At that point the CM will direct her on where to exit the loading area and wait for you. She should not have to wait alone for more than 10 minutes before you appear.