Welcome yo HCM and thanks for your query.
Serum Sodium levels to increase needs water restriction than increased sodium intake.
Water needs to be seriously restricted to 1 to 1.5 litres only for 24 hours including other drinks like coffee/ tea.
If electral contains potassium, it is wise to avoid as her SERUM K is already high.
Also renal function has to be monitored, as if the renal function is good, K should not go up.
Kindly take a opinion form a internist/ nephrologist
Hope this helps your mother,