She wouldn't, not unless she studied it, which people of any background can do.
My point is, a rational person knows what they don't know. But when it comes to Christianity, it seems that every non-Christian feels competent to comment on it without studying it. Atheists do so all the time.
Rand ping.
Ayn Rand opposed all religions including the Judaism which she did fully understand—and was very open about it.
Again given the way Jews were treated in Czarist Russia I doubt she was motivated to learn anything about Christianity.