I do not know about Florida, but in my state a person can be legally served by the attorney publishing the service in the Legal Notices section of the local newspaper. If they do not know exactly what city she is in they can publish in several papers. They would not need to hit every paper, just the main ones, to be considered legally served.
Again, not sure Florida allows this type of process service...but surely there are from time to time Florida residents who must be served for whom a current address is not known. How would a homeless person be served in Florida if they could not be physically located?