Sister Is Threatening Legal Action And Child Protective Services

In Texas. 8 years ago my sister voluntarily signed her rights away to her son and I adopted him. She has always been a rather absent mother and has dealt with legal, drug, and mental health issues. She has a wild hair up her you know what and now is threatening legal action based off being “under duress and coerced” when she signed her rights away and physical abuse, both without merit as she lives 5 hours away and has not seen him in years. Does she actually have any legal recourse? From my understanding in Texas, adoptions and voluntarily signing rights away are final actions. Especially 8 years after the fact.