Since you went pro-se before I am assuming you are familiar with the Florida Family Laws, but just in case here is the link where it can be found online.
I have found knowledge to be my best weapon in court, make the child support guide lines and laws your bible if you have to! I would like to know how she is proposing that you owe for BOTH children when you have had one of them.
Make sure you have documented proof the child has been with you. School and medical records, pictures of her in your house and of her room. Statements from friends and family ect. This is pure idiocy on the part of the court! Best of luck to you.