When it comes to dealing with a government entity, you must accept that most things are very black and white without much room for interpretation or reason. There are some forms (such as the Economic Hardship Deferment) that are based only on the borrower’s information no matter what and there are other programs that if you file jointly you have to include your spouse’s income.
The Income-Driven plans fall under this definition. It does not matter if you and your spouse have separate checking accounts. It does not matter if they are “your loans.” It does not matter if you got them before you met your spouse. If you file jointly with your spouse, you must include both of your incomes.
Now what if you file separately? Well for now that means you can include just the borrower’s income. Do consult a tax pro though as there are some major differences between these filing statuses. Also be aware that one of the elements currently of the new proposed PAYE plan at the end of 2015 is that if opted in to you will have to include spouse’s income no matter what. But again we will cross that bridge when we come to it.