This is so adorable and harmless, you do you. And I think it's so sweet that it gives you a way to bond with your niece! It reminds me of using Disney movies to bond with my severely autistic sister. I began to draw Disney characters for her when I was around 12. She would sit next to me and tell me which character she wanted me to draw. She wasn't very verbal, so it was our form of communication. It was really the only way I had to engage with her for YEARS. She would watch them on repeat 24/7, I have most of the early movies memorised line for line at this point.

Fast forward, I'm in my 30s and still secretly obsessed with Disney, my husband doesn't mind either. We sit and watch Disney movies with my sister when we see her (she is 26 now). For me, Disney is my childhood with my sister and I am always going to be very fond of the movies. And drawing the characters with her taught me how much I love art, I ended up getting a BFA in studio art and am now an artist/teacher.

So, you never know how these interests can have lasting, positive impacts in your life. Just go with it:)