"I'm just posting this for your benefit, in case you were living under a rock this whole time." <-- what if I'm brand new and didn't know who Talfryn was until he said something in the G1 thread?
So Lyn's dad probably stopped in Gwaren a time or two to trade or restock... he might know her from that.
And then Roran's never left Redcliffe so this whole darkspawn attack going on there will probably have been the first time she's met him.