You have 90 days to marry or her visa is no longer valid and she is supposed to leave the USA. If she does not leave as the visa requires then you may contact ICE. However, it is up to ICE to initiate removal proceedings.
If she refuses to leave your home you may need to go through the civil court. In the event that it gets to that point contact a domestic/family law attorney.
If it's not working out, then the first thing to do is to simply tell her and facilitate her departure civilly if possible as that will be the least stressful for all concerned. If she refuses to leave then you my need to seek a restraining order or other means of non-voluntary removal. If you don't complete the marriage process then her basis for legal status no longer exists and she is required to leave the country. Advise ICE and let them handle it.