Mosi has an eosinophilic granuloma (confirmed by biopsy). A quick Google has confirmed that rodent ulcer, eosinophilic granuloma and eosinophilic plaques are all part of eosinophilic complex. I think they are just different presentations and all are underpinned by inflammation, hence steroids helping.
I think that fortunately Mosi does not get the itching or the scabs. For a while he had what looked like a large pimple in between his nose and mouth but that appears to have gone. I asked the vet whether that was likely related to the granuloma in his mouth and she said likely. He has a different vet now, but none have really been over worried about Mosi or suggested he has any treatment for it. I don't know whether it is still there as it would take sedation at least to examine the area given it's location. I take the view that if he is ok, I won't worry about it. Obviously your girl is affected much more severely.
Regarding food - I feed raw. Have you tried an elimination diet? I think the difficulty with this complex is trying to locate the cause as constant treatment is difficult (steroids not being good long term) and barely keeps on top of things. Elimination diets are difficiult to do as it requires finding a novel protein if possible, or at least avoiding commonly used proteins, and feeding that and only that (and water) for 6 weeks before introducing a new protein. I copped out a bit by feeding chicken first as I had a hunch he was ok with that (I should have added that Mosi tends to have problems with diarrhoea but this seems to be under control with his raw diet) and fed a single protein tinned food (Macs I think although not sure). Wsn't 100% sure of it's success but after 6 weeks on that I tried him on turkey and it was then that I decided to switch to raw and see how he got on. Easiest way to feed only the protein and no additives at all. He was fine so I then added a supplement to the meat to make it a complete food. He now has turkey, pork, lamb (he's not too fond of that), duck and rabbit. The last 2 as commercially prepared raw food. No idea how this has affected his granuloma but he is due a dental so will ask them to check then.
Mosi does scratch a little bit more than normal but not excessively. Or at least he did but he seems not to do it much now. I think for him, diet was the answer but it's not for all cats.