Your sister is most likely suffering from diabetic retinopathy -proiferative type which requires laser surgery urgently , if the bleeding is massive then laser may not be possible.always get both eyes checked up. cataract surgery is done when laser photocoagulation is not possible through the cataract. kindly consult aretina specialist for her diabetic retinopathy. the blot clot can take upto 6 months to absorb.