Fortunately I had a cup of ice and a plastic bag, which I gave her. But there is a better solution.
At the 99c store (or Walmart, or expensive pharmacy if you prefer), they have instant cold compresses. It's a small, heavy plastic bag, maybe 4x5, very light, and it contains some kind of chemical crystals. All you do is shake it up and it turns very, very cold - icy cold, in fact. I'm told it will last for 30 minutes or more.
What a great thing to carry in your golf bag. Incidentally, to prevent further injury, should you pop a tendon, drive directly back to the clubhouse. My friend decided to finish the last 4 holes, and two days later, even though the arm was no better, she played another 18 holes with a big ace bandage.
Your body is a 'temple', or at least a housing that should last into your 90s - provided you take care of it. Show enough love to yourself and gratitude for your heatlh, to take care of your body. And when it signals, "I'm hurting," give it a much deserved rest.