You have to refer to your paperwork. If the Order says that she has to pay one half of a bill but does not say how she has to pay it, then it sounds like she has a lot of latitude in making that decision. If you need more specific terms, then you should file a motion to clarify and ask the judge to be more specific with payment terms. You would want to do that as soon as you can, though, before the Court loses jurisdiction and requires you to pay a new filing fee, etc. Good luck.
A weekly guide with tips and legal advice for each stage of the process.