Spleenectomy patients are more prone for infections especially intestinal infections,tats why she has been prescribed antibiotics. by the way you have mentioned Lactobacillus
TZ ,did they were prescribed by the doctor?so whatever be the cause or result,since your mother is passing loose stools every 10-15 minutes its not advisable to take drugs empirically. get a stool(motion) test done and consult your doctor with tat report. hope this wil definitely solve your problem.