If I am reading this right, @Madalynn1, you are trying to cancel after the original check-in time? That will be why it is not working for you. Even a flexible cancellation policy requires that it be 24 hours before check-in. But as I say, I may have misunderstood your post.
It doesn't matter, because in any case, all is not lost. You can contact Airbnb and explain what you are trying to do and get some help. Go through your itinerary to do that. Don't pressure your host to do it. She has much more at stake - trying to cancel from her end will result in penalties for her. If you are the one wanting the change, it is you who have to do it.
All the best!