My Dad had his done at age 79. A big age difference I know but he was in very poor health at the time. The procedure only took a short time, we waited in a waiting room. They made a small incision, removed the old device (they simply unhook the leads), cleaned out the "pocket" where the old device was located, hooked up the new one and put in a few stitches. They did the programming and he came on home. Still had to keep the arm down for a period of time but it was pretty easy for him.
She will be tired afterwards so be prepared for that. It took a little out of my mom who was only 69 when she had her second pacemaker.