In the case of your sister-in-law the condition is called extra-hepatic portal hypertension. There is risk of blood vomiting in the long term. Also since her spleen is enlarged problems like anaemia which you have mentioned are likely to recur. However the treatment is not only splenectomy but some other procedure like a shunt or a non-shunt operation for treating both the enlarged spleen and the portal hypertension at the same time. Splenectomy alone would leave the portal hypertension and the risk of bleeding from the gullet untreated. At her age the risk of the surgery is low. There are also other options without surgery to treat the risk of bleeding which can be combined with a splenectomy. I advise you to consult a gastroenterologist for advice in this matter.