I wanted to post a follow up.
On another forum someone pointed out that the spinning looks similar to when these frogs are trying to shed and remove old skin. This got me thinking, and I watched back in the video I recorded to see the exact way she would spin around. Whenever she starts it up she always goes to the left, the same side her injury is on.
Now I have no idea why frogs would exhibit this behavior, as these ones don't have teeth or even a tongue, but it made me think of the way an animal would try to lick its wounds when injured. So is she just aware that there is pain on her left side and trying to reach it somehow... but it being right on her face she's never able to reach it and keeps spinning? I don't really know for sure, don't even know if these frogs would have some similar behavior.
But this could explain the bizarre spinning thing which I can't find any info on elsewhere, and wanted to keep this thread updated on that regard. So far she's still hanging in there, but as she still refuses to eat I feel like her activity level has started to drop. Hoping she recovers enough to get her appetite back before much longer. Still no signs that there is an infection that has spread anywhere else for now.
I might try to see if I can find someone nearby who will examine these frogs and confirm whether or not it is a physical wound. It was my first thought when I saw the injury but I couldn't fathom what could be the cause. Now I'm starting to suspect that it may have been the work of one of the other frogs. They can get into fights during feeding time, just today I noticed the biggest one latched onto another's leg and was particularly aggressive. Wouldn't let go until I reached in and lifted them both in my palm out of the water for a few seconds. Due to the nature of the bare bottom tank I have them in, these frogs seem to retain their claws. I have no idea how sharp they are, but it seems plausible that it could injure the skin.
I'd be curious to hear from anyone who has kept these types of frogs if they've had any experience with them fighting bad enough to injure one another. I've read mostly that they are non-aggressive and won't harm each other. This has mostly been true in my experience too, but our biggest frog who we've had the longest does tend to get more aggressive than the others, particularly during feeding time. She has tried to grab food from another frog while they were eating it, and I'm wondering if an encounter like that may have been what lead up to this situation.
I'll update again with the outcome or if there are any other significant developments. Thanks for your responses and kind words, BossFrog!