About her being on antibiotics- I wouldn't push food during this time: antibiotics are a little hard on their body & may also reduce their appetite- nothing to worry about, but I'd plan to add reptile probiotics to her prey* AFTER she finishes her course of injections, because antibiotics don't discriminate between bad bacteria or the "good" bacteria in their gut they need to digest properly. (*I assume you don't feed live- best way is just to pack the probiotic powder into the dead rodent's oral cavity.)
Glad it's not cancer- this (abscess) was the more likely issue, so I'm not surprised.