Something seemed off about Hermione today, but Lily didn't think much of it. She was investigating them because they were a little off, wasn't she?
"Fairly good. I actually had a question for you." She paused to think for a moment. How would she bring Severus into the conversation? She figured she could bring up Severus casually, hope Hermione reacted (or pretend she did if she didn't), and then ask about it. The only thing she could think of was to ask about school. "Um, you know what we've been working on in Transfiguration? My friend Severus and I have been working on it, and are completely lost. Have you figured it out yet?"
She tried to think of whether she was having trouble in Transfiguration this week. She did have a little trouble getting that one thing, hopefully that would be enough that Hermione didn't notice. It's not like she was watching Lily's every move or anything.