There are some people (so it's claimed anyway) that don't experience the same feeling of desperation will a full bladder, or they can maintain a full bladder for a long time before intense desperation sets in.
On the balance of probability though you're probably right to have your doubts Dave, especially if she didn't seem into it at all.
I remember it causing a stir at the time though with many excited that you might have found a model that could hold a full bladder for so long.