Awkwardness

Backstory:
I am student teaching at my old high school, with actually, my old Latin teacher. My high school is very traditional, and requires that students call teachers Mr. Smith or Ms. Doe. So I went there, and all the teachers were "Mr. Marcovitz" (I am making up names left and right.) or Ms. Jacob.

Current Conundrum:
Fast forward to student teaching, and I was talking to an old English teacher, and she told me that as a colleague, I was expected to call her by her first name. My reaction was "I don't know if I can!" It is weird to shift from basically an authority/non authority to a equal footing relationship. I don't know how I feel about it.

Conclusion
So far, today, when I talk about the teachers, I still call them Ms. Jacobs or whatever, but when I talk to them I force myself to use their first names. I guess it's ruder to not say their names at all!