She's not receiving backlash for having a pro japanese Great Grandfather. She's receiving backlash for bragging about her Great Grandfather in every interview like she's proud of his wrongdoings.
This is the problem with dramas featuring popular actors.. You can’t even express your opinion. If you do, you’ll get mass attacked by their obsessive fans who are 24/7 camping in the comment section.
“Oh so you don't like burgers?”