I'm not an expert on Florida standardized assessment, but I reviewed the website fairly thoroughly and it looks like your daughter is required to pass both the Reading and Mathematics sections of the Grade 10 FCAT before she will be allowed to graduate, but if she should fail a section, she only has to retake the one section, and she has multiple opportunities throughout her eleventh-and twelfth-grade years.
Otherwise, in all other grades, the FCAT is used only for measuring the extent to which students achieve the curriculum standards set forth by the state. As you have probably heard, each student's performance on state standardized assessments are tallied, providing information on how well each school is doing in terms of meeting the state curriculum standards and expectations. For more on this, please see: http://www.fldoe.org/faq/default.asp?Dept=179&Cat=95
4th grade is not a mandatory retention grade like 3rd grade. Fourth grade FCAT is the first year the students take the Florida Writes test and are asked to short and long response on the FCAT. If you daughter is performing in class then she shouldn't have a problem. You may want to have a tutor, if possible to decrease anxiety. That is what several of the parents in my class have done and it works wonders.