Lizzy carefully stepped out of her room that night with that neatly thought out excuse that she gave to her husband and with what she said, she wouldn't give Sylvester any reason to suspect her. She was of course going to check on her sons Tyler and Liam but she didn't plan on spending so much time in their rooms and as a matter of fact the only reason she wanted to come out was to see Mario. Even if she ended up staying long hours in his room, no one would suspect her or bother checking up on her since she was his step mom as well.
After briefly checking on her sons, Tyler and Liam, she went straight to Mario's room and gently knocked on the door.