Worried about ER claim being denied

Context: At the time was living in California, with a Highmark BCBS plan that was covered in the area. Same plan still but we have moved.

Wife woke up with severe abdominal pain. First thing we did was call Teledoc and describe the symptoms, and the doctor with Teledoc said likely Appendicitis. Dr told her to take 4 ibuprofen and wait 2 hours to see if the pain goes away, then go to Urgent Care.

Waited 2 hours and pain persisted, so we went to Urgent Care. Urgent Care doctor asks to describe symptoms and immediately also says that it is likely appendicitis, stating “I would bet money on it.” Asks my wife to provide urine sample and discharges her and tells us to go to ER immediately.

To make a long story short, we go to ER, they run a bunch of tests, ultrasounds, etc. and they cannot find anything conclusive. The ER Dr. says that they ruled out anything life threatening and even checked for ovarian cysts which were not present. We go home after that.

About 6 weeks have passed since then, we have gotten claims back from urgent care, imaging center and the Emergency Room Dr., all of which were approved, but we are waiting for the hospital claim to be approved or denied. Was told it is about $18k in charges presented to the insurance company.

My worry is that since it ended up not being life threatening, we will be denied our claim and be on the hook for all of that money. Does anyone have insight as to what the odds are of this happening, and if there are any specific laws in CA that prevent this? I know Highmark has done this sort of thing in the past.