I spent the rest of the day occasionally mulling over just how happy I'd be, if I ever needed CPR, if the person delivering it had been certified by a computer program. Oh, well. I suppose I wouldn't actually refuse it. But, still.
I'm pretty sure it's something to keep the bureaucrats happy. You didn't describe why your sister needed the certificate. It's probably something where someone deemed it a "good idea" if a number of people in a location/occupation had some knowledge of CPR besides what's shown on TV. The certificate indicates that said person has some knowledge beyond what Hollywood shows.
A practice dummy would be better, but a well-done computer questionnaire would be better than nothing. In this case, it's a renewal, so it may be to go over some knowledge items (when, how fast, what else needs to be done, etc.)