The recovery after a stroke may not be complete in every patient and your mother probably has some residual neurologic deficit. Physiotherapy should help in improving the facial asymmetry. Secondary stroke prevention is equally important. Hypertension and Diabetes are major risk factors and should be kept under check. Various drugs have been found to reduce the risk of recurrence, especially anti-platelet drugss, ACE inhibitors and Statins. You should consult your Neurologist for the same.