There should have been an Asset Purchase Agreement with the business acquisition.  If properly drafted it should have addressed acquisition of the business name, any intellectual property (such as trademarks, tradenames, copyrights, etc.) along with all goodwill, assets, property, and accounts recievable of the business.  It really depends on what you negotiated and purchased as part of your deal.  If the agreement is silent or there is no mention of the subject then you arguably only purchased what is documented.  However, your filings may have perfected your right in the name first in time, if she did not file anything to establish her right elsewhere.  You may need to enforce your right to use the name based on your priority of ownership through the filings.