I know what you want but I needed to go step by step finding her US records to find her arrival manifest and a place of birth since you were not forthcoming with it.
Since the location is in Croatia, I would suggest putting a query on Croatia's board.
I do believe I passed on a Croatia FACEBOOK forum url but here it is in case not.
Croatian Heritage and Genealogy Facebook Grouphttps://m.facebook.com/groups/1491621441073063
Did you request Florence's SS-5Form? I would think she put down her parents names as well as mother's maiden name.