She knows. Sensei absolutely knows xD But I honestly feel like she's also waiting for Mako to fully grow up, old enough and figure herself out.
May this isn't as deep as I make it out to be xD But I like thinking that Sensei also wants Mako to figure out whether she is actually in love or just has a bit of a big crush on her kind teacher and chosen to indulge her a little while setting the boundaries rather than be cruel towards hers.