I finally decided to give her the opportunity, just until she finds the blue firefly. She's found all of them now, except the blue one. The purple one was off wood street, at the edge of the mountains, about halfway between the arboretum and the Craftsman's Mansion house. So that's another place you can look if you ever need them again.
Thanks for the link to that page. There's a link on that page to a list of which items every spawner produces. It will come in handy for more than just this sim's game. For her, I'm going to keep checking until whatever spawner that's already in the town produces a blue firefly. She has plenty of other things to occupy her time until she finds one. Right now she is on potent invigorating elixirs, working day and night trying to finish making enough large inventions to meet the skill challenge. I'm more tired of the length of time that's taking right now, than I am of waiting for fireflies. While she's working through the night, I look for the fireflies, and interrupt her to send her after them if I find any she doesn't have. Hopefully, it won't be long now.