Hello,
Hm, it does somewhat look like a burn but, it could also be a spider bite perhaps.
Do you know if crickets are ever left in the tank, they are terrible culprits of bites that usually
get infected.
If you have some raw, or manuka honey, you can go ahead & put some of that on the wound
to help with infection right now.
Is she eating normally?
I hope you are able to find a vet.
Tracie