Your mother could be having speaking issue due to multiple reasons 1) she had a silent stroke which resulted in weakness in one side of her face or tongue and so on 2) she has a degenerative condition which might be causing her memory to erode 3) she might have had brain damage to the language centres in the brain leading to problems understanding or expressing language correctly but her memory is intact. First she needs to see a neurologist/ cardiologist to rule out any physical issues. Second she should see a speech language pathologist/therapist who can recommend exercises for her speech and language to improve. Degree of improvement will depend on intensity of the problem and how intensive the speech and language therapy can be.