That Duba'ah wanted to perform Hajj, so the Prophet Told here to stipulate a condition, and she acted upon the command of the Messenger of Allah.  

أَنَّ ضُبَاعَةَ أَرَادَتِ الْحَجَّ فَأَمَرَهَا النَّبِيُّ ﷺ أَنْ تَشْتَرِطَ فَفَعَلَتْ عَنْ أَمْرِ رَسُولِ اللَّهِ ﷺ