Watching wasn't nearly as interesting as doing, and she'd probably get distracted halfway through and let her thoughts roam and drift ... but she'd at least try to pay attention. It wasn't as though she didn't know how to do it; she'd done it before. Maybe she hadn't conveyed that part completely? Or at all ...
"I don't mind asking her. I just ... didn't want to bother her today. She's ... busy, you know?" And she'd looked kind of worn out the last time Lily had seen her, so she hadn't wanted to further burden her with this. "I mean I can do the potion. I made it in school. I just thought that as long as I had someone around who could do it better than me, I'd ask. I'm not exactly top of the potions class." She shrugged and managed a sheepish little grin, but it was true enough.