Is this fraud? Or legit?

Over the summer, I took my daughter to an urgent care for treatment. She is covered under my employer’s PPO plan, but I recently received the bill and nothing was covered. The reason given was because she had other primary insurance. My daughter lives primarily with her mom in another state. The mom sent me a copy of the other insurance card and it has her ex-husband’s employer listed on it, not the mother’s employer. Their divorce was finalized back at the end of 2022 and 2025 is just around the corner.

Is there a legitimate reason for how my daughter can still be covered by her former stepfather? Or is there probably some kind of fraud going on?

I always thought one had to be legally married to cover step kids, but maybe I’m wrong. Is that accurate or no? The bill is a bit steep so I do want to resubmit the claim but I also don’t want to unknowingly do anything illegal.

I am going to ask the mom about it but I want to make sure my ducks are in a row (in the past I’ve caught her being dishonest about things like school registration)

What would be the best way to handle this? Calling my insurance company? Or calling the other insurer ? Or just have provider re-submit the claim through the other insurer?