Suggest Treatment For Swelling And Pain In Ankles And Left Calf

my moms left calf muscle one day about 5 or 6 days ago, decided to cramp up. she says it feels like a constant charlie horse. her left calf is hard as a rock, about twice the size of her right calf, and its starting to make her left ankle swell up even. its very painful for her to walk on. shes been putting ice on it for the past couple days and the swelling and pain is gone/down when she has ice on it, but once shes had it off for over an hour it goes right back to swollen and painful. she hasn't done any sort of intense physical activity lately like sports etc. just typical walking. please help answer any of these questions
-What could it be?
-Is it serious/should she see a doctor?
-What can she do to help it?