When turning in the first ant, she will take a plain green ant instead of the red ant if you have one. However, only the plain red ant will update the first step.
If you already have one of the items needed for the quest in your possession when you reach a step, you can force the quest to continue by selling an item to a vendor and then buying it back.
You can also give the item to a friend and have them give it right back will update as well.
This Quest WILL drive you mad, because the Striped Red Ant is hilariously rare, and then she tosses the first one away and asks for one more... expect spending months in Thundering Steps to finish this quest. Not really worth it unless you have a fetish for spending endless hours hoping that just ONE would spawn.