Did she give you up for adoption? I know many people look for their biological parent and it’s their right. But I also think that when biological parents give up their kids, they stop being parents and by logic of that they don’t necessarily want to be looked up or found. Perhaps it’s their right not to maintain connection with bio children. If they wanted to remain in bio kids lives, they’d not terminate their parental rights. I understand it’s painful but that’s usually what happens, unless it’s open adoption.
It’s possible she didn’t want to be found when she was alive and her grave when she is dead. It’s sad but maybe the only way to go about it is to accept it. Are you seeing a therapist about it?