Don't fry your broody yet!
If there are ants in the nest box, perhaps she left because of them. You say they weren't there earlier, but maybe you just didn't notice, or maybe they weren't active when you looked before.
On the other hand, they may be attracted by the pipped egg.
At 97 degrees, the eggs will be more or less okay for a while, but if you want to save them you'll need to do something soon. There are lots of folks on here who can tell you lots of ways you can try to save them. One way that's gotten some attention lately is to stick them in your bra (yes, seriously). It's not foolproof, but it's low-tech and can sometimes work.
The one that has pipped, you may be able to help hatch if he doesn't make any progress. Is the chick alive? You should be able to see movement and/or hear pipping from time to time. If it's alive, watch for progress. Moisten the membrane somehow and you can even give the chick a drop or two of water to drink from the tip of your finger. If there's no progress over several hours and/or the chick seems to weaken, you can help it hatch following directions that you can either google or search the forums for (I'd put the directions here, but it's been explained by better experts than I am, many times over, so your best bet is to search).
Even if the broody did abandon them for no apparent reason, it may just have to do with the time of year (Fall is an unusual time to raise a batch of babies) or with inexperience--is this her first time setting? She may do better the next time.
If I had to guess, I would say those ants have been in and out of her nest box, and that's why *she's* been in and out. You could also try moving the nest to a safer place and see if she'll set. Since it's hot out, you have a little time to wait and see. I know *I* wouldn't want to sit in a nest full of fire ants. Yikes!
