To know this is very simple. Normally when a had sex her vagina will go back to the usual shape after an hour or two. And if she has not had sex for a very long time it will still go back to the normal shape. The problem is how to detect the normal and abnormal shape.
you will struggle to penetrate her at first but it will get widen inside the moment it pass through the main vagina opening.
it will hard to penetrate both from the opening to the main vagina hole.