She was ignorant of, or dishonest about, Christianity. She said something life, "You take your ideal man, and torture and kill him. I think that's monstrous."
She just didn't get it. Didn't understand the whole point of Christ's sacrifice. She talked as if Christians advocated torturing all ideal men, as if it were even possible for any man to equate with Christ.
I'm also certain that, like many atheists, she never studied Christian theology, yet felt perfectly competent to comment on it. Not very "rational."
No one is perfect.
L
She’s a Russian Jew! Ayn Rand is her pen name. Her actual name is Anna Rosenbaum. So why would she know much about Christianity? As a Russian Jew her and her family’s experience with Christianity (Russian Orthodox variety) is not likely to be positive.