I would say yes. I was the cool gf to my now SKs. It has been a horrendous transition. Once we moved in and got married (after years of being “cool gf”) I had to slowly start the transition into stepmom, which meant being more of an adult in the home. Doesn’t help that their mom is an absent party girl who only has them 4 days per month, so I was basically their full time care giver. The now preteen SD hates me (she used to love me and want to be me), because she’s think things like “please wash your hands after the bathroom” and “please put your sweater in the closet instead of on the living room floor” and “that’s enough sugar before dinner” are me being mean. It’s been so so so difficult.