However, one reason she might have been hesitant to answer the question could be the fact that Sherwood and Hyland have been dating for two years and there's no reason to upset your show's newest castmember.
Hyland announced the news on Monday in a video she posted to Twitter. "Yup, you heard it Shadowhunters fans, I'm gonna be on the show!" the 26-year-old actress exclaimed. "I can't say who I'm playing yet because it's a secret."
McNamara was equally evasive regarding details of Hyland's character, but she did explain how much of a relief it is to be able to talk about her joining the cast.
"We've been keeping that so secret for so long. It's been so hard," she explained. "I'm really proud of us because we've all been so excited about it and it's been really hard to keep it secret, but she's been a part of this family since day one. And so having her on this show was only natural."