Ultimately the at-fault driver and the driver's bodily injury liability is responsible to cover your sister's bodily injury claims, IF they have BI coverage.

In Florida, bodily injury liabiity is not required though. PIP is intended to cover personal injury protection before BI is used. If the driver of your sister's car has PIP it would be primary, then your sister's PIP would be secondary (supplemental). Then, the at-fault driver's BI would be tertiary (supplemental).

If there is no PIP or BI to cover the claim, you will need to seek damages from the at-fault individual through the courts.

Have your sister and the driver to get PIP insurance through CarInsurance.com.