In Va, can I sue to recoup separate property?

Such a claim to recoup this money is not likely to be successful unless you had an agreement with the person that she would repay the debt.  When you helped pay your ex's debt, it was a gift so to speak and you did not - at the time - have any expectation that she would repay you.  Unfornately, the court is not going to enforce such a claim.  Therefore, i suggest that you look at this as a loss and move on.  its frustrating, but there is nothing you can do unless there was a promise by her that she would repay you.