That is so scary
So glad that she's okay, omg!!!! Thank goodness you were home and didn't run out for something after bringing her in! Geez, maybe we should spread the word around here that when bringing your dogs in, to stick around for 15 minutes or so to make sure they haven't encountered anything while out on their walk. You must have freaked, I know I would have been in a panic!
I would definitely avoid that particular spot anyway, regardless of what may have caused the reaction. If it wasn't some kind of sting or bite, it might have been some kind of chemicals and you won't know if they use that stuff again in the future. Might be time to find a new place to explore, perhaps walk around without Amara and look for anthills, bee's nests, pest/lawn company flags, etc.