It might be MRSA if it’s that resistant to staph. I empathize. I just had cellulitis (bacterial infection of tissue) in my ear and it cultured and even NOT being staph, it took 3 different rounds of antibiotics to settle the infection and I still have post-infection inflammation in the cartilage. These things can be so nasty and hard to get rid of it and I can imagine the child is very stressed and frustrated about returning to the hospital but strong IV antibiotics may be the only way to really get rid of the staph if oral ones failed.