Thank you for reading! and sorry for the late response, I've been a little busy these days. And yes, it's basically for the reason mentioned above;
“Sensee” is a casual, affectionate way of saying “Sensei.”
In the manga and LN, Togawa refers to Itsuki as「せんせ」 (sense), instead of 「せんせい」 (sensei), so she’s basically saying “Hey, Teach!” instead of “Hey, Teacher!”