God I STILL get the 'not a real woman' schtick because of the SAME thing. I'm geeky, have a deep, 'strong' (not-feminine) voice, work in a typically not feminine type career (CODE MONKEY! slams head on keyboard WORK CODE WORK!), and have a deep dislike of most romance and chick-flicks and a strong enjoyment of action, sci-fi, and horror, and have a secret desire to do Muay Thai just cause punching people in the face sounds...so much fun.
I got the whole "You're pretty, I bet more dudes would like you if you stopped acting smart all the time" speech as a teen from multiple people. Even my husband, who I love, and who I know says this in jest, also says that I am more masculine. So I feel for your sister and ooof it's frustrating cause I like pretty dresses and bright colors and cute things too! I just think princess should be allowed to wear the pretty pretty dress while riding a dragon into battle and being coated in blood...that's all!
ALSO, RANT INCOMING!
Back in the day (and still very common), the Default human person was MALE. Thus women were written as love-interests, maybe even COMPETENT love-interests, but were centered around the self-insert MALE hero.
This has changed a lot now a days, at least in some western media and japanese media, which is GREAT...BUT.
BUT.
Not only was the default MALE...the default...and I'm gonna bring up the race card, sorry, the default was also Anglo-Saxon WHITE.
So, even when reading or learning about romance novels with self-inserts, I could not insert myself into the protagonist because I'm a WOC. I'm a biracial Puerto Rican military brat with bi-linugual parents who have SUPER THICK accents.
I would never be the hero.
I would never even be the love-interest.
I would be the sassy, spicy side-character who offers nothing but token one-liners and support. OR the treacherous, overtly-sexual (thus whorish), jealous harpy who stands in the way of the self-insert LOVE!
...So there were a lot of stories I couldn't really relate too. How I can insert myself into the 'self-insert' when I could never BE that self-insert?
So already, I immediately have a stick up my giant ass on romances with blank-slate protags because I am obviously not meant to be the "blank-slate". When the boring protag that every loves has 'dull brain hair that hangs over her pale face", I'm out of the running. My butt is too big (even when I was a teen), my hair is too curly, my skin is too dark, I'm out!
So yeah I couldn't be in romances already because romances were not made with me in mind, thus I can't relate. Since I can't relate, I hope that the MC is at least interesting.
Lo behold, how can they be interesting when they don't have distinct hobbies, or a different routine, or a unique personality? There is nothing about the MC that makes them stand out because they are a so-called 'self-insert'.
Thus most romances, and some other genres, that have self-inserts MC are not my cup of tea. Thus why I take most harem animes (with female or male MC) as well.
/rant