Can a dual citizen child be blacklisted for overstaying in Thailand on a British passport?

Looking for advice for a more complex overstay issue. One of my close Thai friends recently passed away from a battle with cancer. He was previously married and had a child with a British citizen. While he was receiving treatment his daughter who is 12 year old flew over to be with her Thai father. It has just came to our attention that she entered Thailand on her British passport in December and received a visa exempt stamp of 60 days on arrival which has expired and put her on 5 months overstay. She does have a Thai passport but apparently this has also expired. She is due to fly back to London on the 22nd of this month. Is it possible for a Thai citizen to overstay in their own country as a dual citizen? As this is 90 days overstay can she be blacklisted from a country she is a technically a citizen of? Is there any leeway as she is still a minor and her Thai father who was dying and her soul carer at the time didnt organize her extension? Thank you.