Answer:
substantial business between Barbara and Sarah through Sarah's website.
Explanation:
A person cannot be brought to the court if the person belongs to some other state than the place where case has been filed against him. A court doe not have any jurisdiction over a person if the person is resident of some other state and the court is in some other state.
In the context, Barbara files a case against Sarah in Washington court. But Sarah is not a resident of Washington. Sarah has a website which can be accessed in Washington. Now the court in Washington can have jurisdiction over Sarah only if the claim of Barbara arises any substantial businesses between Barbara and Sarah through the website of Sarah's.