Her anniversary is accepted, mine is not. Even duo does not want me to get married :p
Is it not possible to write "o meu aniversario"? I've noticed other sentences where they use the a/o article even when it does not get translated as "the" in English. I think I can remember an example: "O homem le as suas cartas" (why does "as" work here, but not "o" in the above sentence?)
No, you can't have both "today" and "it." That would be two subjects in one sentence, when the pronoun "it" is supposed to replace "today."
I have already put aniversario for birthday and it was wrong --it should have been dia de anos NOW birthday is aniversario are they both correct or not
«aniversário» is any "anniversary;" if you don't specify, it means the same as «dia de anos». If you specify, e.g. «aniversário de casamento», then you would specify in the translation → "wedding anniversary."