In response to my post on a Croatian forum, I received an e-mail from a person who lives close to Skradin. He is offering to help search for Seka.
He says he is very familiar with Skradin, as well as with Belgrade, and has friends in both places.
He also says that Serbs generally did not sell their houses in Skradin due to the war, so he believes it is likely that Seka's family still owns a house there. However, he is going to check the Land Registry for any registered house sales and any other information which could help identify Seka and her family. He will also talk to older people residing there.
I will let you know what happens.