ID: Drawing of a duck billed platypus underwater, they're wearing a rainbow coloured t shirt and a pink bum-bag, and saying: "Ally is not something you can self-identify as, it's a title that you earn. Let your actions speak for themselves!"
Credit: Sophie Labelle
The point is - if it's for your sister... Ask your sister.
The feeling of "What am I supposed to do?" is totally natural, and something you have in common with a lot of queer people. The simple answer is "Your best".