This link indicates that she would need to pay a $15 late fee and renew in person with documents:
It also says you should contact your local DMV office. Here is the DMV guide and some additional information:
As your sister is out of the country and unable to renew in person, I would call the Florida DMV, explain the situation and see if there is another way to renew her license. I hope this answers your question. If not, then please reply and I will provide additional information. Thank you.
My sister will be here, in Boca Raton, FL, this July, so she can renew in person. She has her expired drivers license and a passport. What, if any, additional documents will she need? Will she have to take a written or driving test? Will we be able to make an appointment in your Deerfield Beach office, on Hillsboro Blvd? Thank-you in advance for your help!
Those in this situation must renew their driver license in person at a local drivers license renewal office. Bring your expired license, birth certificate or passport, and a cash or check to pay the renewal fee plus a $15 late fee. Some situations may require more documentation, so it's best to call the office before leaving home to make sure you have all the necessary identification.
I hope this answers your question. If not, then please reply. Thank you.