If at the time, you told her that you would not bill her for the work, you can't bill  her now: you can't go back on or change what was then agreed to. If you did not agree to not bill her for those services *and* she understood (or at least was told by you) that you were doing work for which she could be invoiced, then you may bill her now and, if she does not pay, could sue her for the money, since you are still well within your state's "statute of limitions," or time within which you must bring a legal action.