At first glance it might appear that this is permitted, provided you do not explicitly specify that your friend should sell them on Shabbos. The Shulchan Aruch OC 245:5 states "It is permitted for a Jew to give merchandise to a gentile to sell for him, as long as he does not instruct him to sell it on Shabbos."
However, the Mishna Berura there §21 elaborates that if the market day in that locale is on Shabbos, it is understood that the intent is to sell it specifically on Shabbos, and it is equivalent to an explicit instruction, which is forbidden. From your question, it would appear that this is precisely analogous to your situation.
One possible solution would be to sell the pottery to your friend prior to Shabbos. Then, all the items she would be selling are her own, which is permitted. The Poskim (Minchas Yitzchok 3:29) even permit this when the non-Jew is selling it on commission and can return the unsold objects after Shabbos. Since at the time the merchandise belonged to a gentile and they would bear responsibility for any loss or damage, it is not considered selling Jewish property on Shabbos.