If I'm guessing right, hyesung's mom is an omega due to physical and verbal abuse, she left her husband and thinking that since her ex-husband is well off, he could take care of hyesung more than her (in terms of money because she might've run away without anything in hand and carrying a five year old would just mqke the both of 'em suffer) especially since she thought he's an alpha too, then she might've look for him but might've been blocked by the scum ex-husband, knowing that her son married dojin, she might thought tht dojin most likely would be able to help her that's why she went to the agency instead
My man will be diagnosed with some stomach problem before the end of the story