It doesn't mean anything, stop imagining that it does. You might be sitting somewhere right in her field of vision, and she's not actually looking at all. Licking her teeth? - just cleaning away the last of her coffee. For all you know she might be thinking you look like someone she knows, or at her age she taught your dad, or she's mentally making her shopping list.
Give this up - it's more than her job's worth to have any designs on you or any ideas about fancying you. Lots of kids have crushes on their teachers.