@jfles00 I’m sorry things are so tough with the insurance.
Could your younger child be covered with CHIP?
You might have to pay premiums (depends on income) but then maybe it would cover her weekly treatments and the rest of the family could be on a cheaper plan?
I think it covers dental as well.
https://www.insurekidsnow.gov/coverage/ar/index.html
Also, are you and your husband both self employed? Maybe it would be worth it to get a job with employer group coverage and that might bring the premiums down?