Taliyah met both Riven and Yasuo

In her long lore, it read, " but it was a fallen captain who swore to take her to a wild place across the sea, a place where she could hone her abilities without fear, who made the most convincing case."

Riven was a captain in the Noxian army at one point before she decided to put herself in self-imposed exile.

We just got a relative time confirmation of around when Riven may have left Noxus which would have been during the winter months.