I'm surprised myself and I agree with you. I'm sure she wasn't but just isn't saying anything. Developing her tits earlier and before her older sister did and still having bigger tits than her older sister is something I would envy if I was in her situation. My former in-laws including my former mother-in-law told me they were glad not to have my size boobs, a size 42, but my former mother-in-law said she was also glad that I have bigger tits than her and made light of it to everybody.
I'm sure it's curiosity. Everybody has a passion for those things whether you're a girl or a guy. Contrary to what most of you are saying, I was the first one in my class to have to wear a bra in 4th grade. A 38-size no less when the rest of them were still flat-chested. The rest of my female classmates and girls older than me teased me for being the only one in my class to wear a bra. And yes, I envied them for being flat-chested and some of the tits who were older than me and more petite than me.
Consider yourselves lucky. I was already wearing a 38-size bra when I was only 9 and the first in my class and School to do so when the rest of my classmates and the Elementary School girls my age and older were still fat-chested. I went up to a size 42 by the time I was 12. The other girls made fun of me for it.