1. The population density of Iowa is low, so that means there are less people to sell goods to in any given place.
2. I have no idea where she is from in Iowa, she could live in Smallville population 300 for all I know, of course there is going to be no market for fish there. Not really fresh anyway.
3. Just because one woman says '...but in Iowa we don't get fresh ingredients like this,' doesn't mean it actually isn't possible. It would probably only be in large population points though.