Some would argue that Trewlaney knew very well that she would be having a guest - she'd gone and made an appointment to see Lavender hadn't she? But ahh, it was the inner eye that told her she was going to have to do so to begin with. Fates told her today was the day she had to be meeting Lavender Brown, and so that, of course, was why she'd set the date. Just as fates told her she would need tea and perhaps even her crystal ball for this meeting.
So when Lavender arivved, Trewlaney had just gotten up to just pour the tea. She set a cup down next to where she'd been sitting and set another down across from her, next to a another purple pouf for Lavender. "Hello Lavender, dear," Trelawnney said warmly. She was fond of Lavender for several reasons, one of which was the fact that the young woman had always been such a staunch supporter of hers. "It has been indeed. Shame that our fates had not entwined until this day." She peered at Lavender through the steam rising from her cup as she carefully held it up to inhale. "Please sit. Your tea is just there."
She didn't bother to correct Lavender calling her professor. She'd tried to encourage a more casual friendship now, all things considered, but it didn't take a prophet to see Lavender was still too set on calling her professor out of respect.