Fiancés daughter

His daughter is 18 and tells our toddler that she’s going to smack her. Obviously I don’t think she’d do it but she’ll say it when she’s frustrated at her. She also yells at her when my daughter is doing something She doesn’t like. I’ve never said anything because I’m trying to not be that bitch stepmom and at the same time I’m trying To think if I had a daughter who her age and she told me I told her that I think she’s just be playing around but because her and I don’t get along I feel like she does it to annoy me sometimes or maybe I’m looking too much into it but if I am or reacting someone please let me know so I don’t take it to the heart