Our nekkid girls were very prone to cysts. Although those pics look more like an abscess, our Rosie had something very similar. It started just like the one on your Jani did (Rosie's was right where a belly button would be). It grew very slowly. After about two months, it started getting ugly like what you just went through with Jani. Our vet went to take a look at it, and it popped. It was indeed a cyst, that had abscessed.
Perhaps this what might have happened with Jani too. i.e. you might not smell the nastiness of just a garden variety abscess. Cysts don't tend to smell as bad.
Our Rosie healed up just fine (with daily flushing and antibiotics) and hopefully Jani will too.
Unfortunately, as beautiful and wonderful as nekkids are, they are also prone to skin "ickies". They are very prone to ingrown whiskers too. :sad3: