"Hypertension" means she has high blood pressure. IIRC, the current knowledge is that one has to be a very heavy salt user for it to have a large impact on BP. If CTY has been doing the low sodium thing for years, as she suggests, the cause is not her salt intake. She should look at her weight and caffeine (e.g. coffee, tea, colas and other caffeinated sodas, chocolate). My speculation would be substantial girth plus significant coffee or tea intake.
Now, hyponatremia (low sodium) can really affect a person's mental state (this isn't a joke about DU-folk). Though her doctor never took things seriously we figured out that my MIL had that problem in her last 12-18 years of life (she lived with us). We realized what was happening when we had to take her to the hospital for a UTI, found her a totally different person the next AM (IV antibiotics in saline) and then watched her descend to her previously withdrawn persona after she was released to a SNF for a few days. It got so extreme on a cross-country trip to KS (a niece and nephew - her grandkids - were graduating from Kansas State) that at one gas stop she asked me if we were about to abandon her on the side of the road. It took the saltiest fast-food (KFC!) and frozen meals to keep her on a somewhat even keel.
So, yeah, CTY's hyponatremia can be very serious, and she should go normal to slightly salty in her food (and lay off the caffeine, and reduce her sugar & starch intake).