My daughter's PO officer said she is going to extend my daughters probation until her fines are paid off. We live in WI is there anyway my daughter can fight this?

The only way is for your daughter to pay her fines. It's an initial condition of her probation and if you look over the initial paperwork she signed, she agreed to pay her fines, fees, etc... inorder to successufully complete probation.

The probation department is correct in extending her probation. The other alternative they had was to violate her for not paying the fines during her given probation period.
Would you rather see her in jail as that is what could have happened or on the outside?

I highly suggest not fighting it as there is nothing to fight about. Consider her VERY lucky that they agreed to extend the probation as they did not have to do this and they could have easily violated her probation. Re-read her original probation paper she signed and see if I'm correct or not.

Yes, actually the PO can violate her Probation for not paying.
So I guess longer probation is better than sitting in jail till it is paid.
She needs to start a payment plan to get them paid, or they will continue to extend her probation or at some point, violate her and send her to jail.