Silly question. It is not for us to determine what is or isn’t sinful. It is spelled out in The Bible. Might as well ask if she believes the Bible.
I think we all know, that the only acceptable answer to question such as this, is to Proclaim that you are liberal on homosexuality, that you believe in homosexual marriage Etc.
These sorts of questions are traps. Unless you Proclaim how liberal you are you’re going to be condemned.
She should have said “I’ve been taught, and I believe that while it’s not my place to judge others, that homosexuality is a sin”.
I.e.- the truth.