hi there, the easy bruising and purple marks could be due to coagulation disorder.In this condition the blood does not clot properly which could be due to a defect the platelets like decreased counts or funtion or could be due to decreased function or quantity of coagulation factors which help in clotting the blood. As she is a known case of stroke
it could also be caused due to medications given to her for decrease her coagulation process. Her legs could be turning purple due to stagnation of blood in the lower limb which is caused due to deep vein thrombosis
which is very common in non ambulatory patients. Her doctor should look into all these facts and take action immediately before some lasting damage occurs. Talke care.