Fearing that he would try to double-cross her, she insisted on going with him. She promised to stay far enough away that she couldn't actually hear the message and Ginny didn't know she was there, but she was going. Part of her feared that if she let him out of her sight for even a moment, he would betray her again. She needed to warn Antonin, to see with her own eyes that he was still all right. Maybe they wouldn't be able to recover what was lost. That didn't mean she didn't still care about him.