Tell your sister that I spent my whole life, from birth until age 53, trying the be the boy and then the man my parents wanted me to be. I got so good at it, and so deep in denial that I convinced myself that I was that man.
Unfortunately this set up a huge and horrible conflict within myself. I suffered from horrible anxiety, vivid nightmares, somnambulism, and immune system issues my entire life, and from chest pains, irregular heartbeats, high blood pressure, TMJ flare ups, neck pains, jaw pains, and inflammatory arthritis for the last eleven years.
During all the chest pains and irregular heartbeats, my doctor and cardiologist found nothing medically wrong with me, and my doctor told me that it was panic attacks, and work related.
When your sister tells you that means it was time for me to see a psychotherapist, tell her that is exactly what I did. I was diagnosed as transgender, and placed on HRT.
HRT fixed everything, except some residual low level panic attacks, and presenting and interacting as female fixed that.
This is not a fetish. It is not sexual. It is not a "lifestyle choice." This is who I freaking am, and I know this because I gave away more than half of my life trying to be who other people wanted me to be.
In order to please my parents I became a lawyer, married twice, fathered a child, raised two stepchildren. I'm done. I paid my dues. The rest of my life is mine. For me. To do with as I please, regardless of the necessity of it or not.
But the bottom line is, I could have been happy and healthy if I had been allowed to choose my own path. And I lived in misery for more than fifty years because I was not allowed.
In terms of facial feminization surgery and other "cosmetic" procedures? I am a trial lawyer. Therefore I am in the public speaking business, and my face and voice are my livelihood. I don't view getting face and voice feminization surgery as any different than a laborer who is born with a hand missing getting a hand transplant so that he can be a better worker.
My heart and soul are female, and I deserve to be perceived and treated as female in public. Therefore I am entitled to have every male gender marker eliminated from my face, body and voice. Frankly, for cisgender females, cosmetic procedures may or may not make them look more feminine, but are unquestionable to make them more attractive.
I don't necessarily need to look more attractive, but I have an inalienable right to look and sound female.
What your sister is trying to do is blatantly manipulative and extremely insulting. Her words imply and she will probably refuse to admit, that she thinks she knows who you are better than you do. She wants you to accept not yourself, but her idea of who you should be. My father was the same way -- and it took five years to get him out of my head after a stroke finally silenced him when I was 46. Don't even think of throwing your life away for relatives the way that I did. No one who loves you will weaponize their words to try to force you to question your own identity.