Insurance denied my daughter's specialty seizure medication - they want her to fail two cheaper drugs first. She's 6 and her current med is finally working.

I'm losing my mind a little bit so apologies if this is rambling. My 6 year old has been on a specialty seizure medication (it's one of the newer ones, brand name only, no generic) for about 14 months. We tried two other anticonvulsants before this one and both either didn't work or caused awful side effects. The current one finally got her seizure-free.

We just got a letter from the insurance company saying they're not approving the prescription anymore as of next month. They're requiring "step therapy" - she has to fail two cheaper drugs before they'll cover the one that's working. The cheaper drugs they listed are the same ones she already failed last year, documented in her medical records.

Her neurologist is on it and submitting an appeal but I'm terrified. The med is $4,200/month cash price. We can't afford that out of pocket and we definitely can't experiment with going off something that's controlling her seizures. What are our actual options here? Has anyone successfully fought a step therapy denial when the patient already failed the prerequisite drugs?