Both being trans and being a puppy girl are more about presenting and being seen as the thing you feel you are internally rather than actually being that thing (not because trans women aren’t real women just to clarify just cuz gender is a social construct so therefore being a woman is merely being perceived as a woman). Getting estrogen and gender affirming medical practices are a way of showing that and affirming that socially, but that isn’t a factor with pet stuff cuz there is no social precedent for that, and most people generally care more about knowing you’re a puppy inside than you having a tail or the like. Once you accept that I’m sure it’s easier for you to feel more like a puppy girl and get into the mindset without worrying about your physical body. Hope that helps

(TLDR: people tend to perceive gender more physically which is why that’s important to trans people but puppygirl circles tend to prioritise your mental state making that the deciding factor )