Purebloods were special beings, and Lea knew they would play an essential role in their future. However, she will let the siblings decide their destiny.
She didn't want to impose her beliefs on others, and she wanted them to see things through on their terms. All of this was necessary. She just wished her family and friends will never deny the obvious truth. After all, if one stays in denial for a long, it will end up causing them pain.
So, she planned to speak with the siblings the next day after they cooled off a bit. Perhaps they will come to their senses and understand that not everything is black and white. The world is full of different colours.