When Yennefer and Ciri come to the broken bridge, Ciri claims it was half a day's ride to the nearest crossing but even in the background of those very shots, there are at least two places their horses would be comfortably able to swim or even ford the river.
When Ciri and Yennefer escape through the portal, they appear in an abandoned building that has no body left alive. There are however two horses for them conveniently tied up outside with no explanation as to how or why they were there.