Hermione was outnumbered to a dangerous degree. While she would confidently fight any two of them together, the addition of a third was cause for concern. She might be victorious, but she really didn't care for her odds. Her first thought was to track down her husband for assistance. As much as she'd always felt confident and reassured with Antonin at her side during battle, he didn't feel like the right choice. She didn't completely trust him when he claimed he wanted his baby brother dead. He might change his mind when actually faced with the chance. And how would he react to Ginny being there? He claimed he wasn't in love with her and Ginny supported his claim. That didn't mean that he wouldn't still feel some sort of obligation to keep her safe. There was also the possibility that Maisie was in the house. Hermione wasn't ready for Antonin to know she existed. Maybe she never would be.