I agree with you, the original sentence doesn't make sense. But if you change it to :" I don't know the answer to whether she will believe us", or better still, "I don't know if she will believe us", then it becomes a lot more understandable.

Thank you, Joe.

You're right, Icespirit. The sentence doesn't make sense, and there isn't enough there for me to figure out what it might mean. Sorry.