Rehabbing a Loan

Hi all. I ran across this forum today while googling rehabbing a student loan, and I'm hoping those of you here can help me. I owe on a loan with Great Lakes in the amount of roughly 32k. I'm in the process of rehabbing the loan (after they already tried to garnish my already slim wages). My worry is the 18.5% that they will want at the end of the rehab. I dont know if I'll be able to afford that. What will be my options then? Would they be able to come back and garnish my wages again? If anyone can provide answers, i would be most grateful.