Again, I grew up in a not only verbally but physically abusive house. There’s no way I would have let my sister get literally nothing on her birthday while I had a huge party and a cake. I also would have made damn sure to apologize to her and wish her a happy birthday. Her entire family not bothering to wish her a happy birthday is really fucked up, and a 15 year old is old enough to say “happy birthday” to her twin. And if you re-read it, she clearly says she’s not close with her twin and hopes she reads it, as in hopes her twin can maybe bother to recognize that what’s she’s doing is wrong.