Stomach ulcers rarely cause blood clots in mouth.What is the age of your mother? Is there a history of cough with sputum or nasal bleeding.The most common cause of oral bleeding is actually nasal bleed which comes in throat.Get an ENT check up done to rule out any local cause of bleeding like oral ulcers,tooth or gum bleeding,any nasal pathology or any laryngeal pathology.Blood in sputum can also be seen in chest infections or malignancy.Do visit a chest physician to rule out any such pathology.