You know what I noticed? Correct me if I'm wrong and you have access to all possible KFP media because I don't and I'd love an accurate count of this.....

Tigress has never called Shifu "Master Shifu" or "Shifu"

She only calls him "Master".

Everyone else in the movies or shows will either mix it up and address him as "Shifu" (mostly Po), "Master", or "Master Shifu". But not Tigress. The only exception to this is in Kung Fu Panda 3 when she straight up just calls him "Shifu" after he gets whacked by Kai.

I wonder if this'll be explored more in the future or if it'll have more subtle hints at the changing dynamic in the Jade Palace....