I want to marry my girlfriend and was wondering if my pre/post marital earnings could be subject to any claims on her debts?.

As long as the debt is solely in her name and your assets are solely in your name, there should no problem.  Your assets are not at risk in a situation such as you present.  However, while your assets may not be directly at risk, they could be if you ever title anything jointly (bank account, marital residence, etc). So just be sure to keep everything separate, at least while you are living in the US.

As for your possible move, this debt is a matter of US law.  It is doubtful that a creditor will attempt debt collection while she is living overseas. 

Note:  A defense often used by debtors is the statute of limitations, meaning the legal time a creditor has to sue you after the debt is charged off. So what if she returns after 10 years and the statute of limitations is 6 years?  The statute of limitations is tolled, depending on your state, meaning that the statute of limitation on a debt is put into a timeout until return to the US, at which point she could then be pursued by a debt collector.