When was the rule about defending with multiple creatures added?

I recently started playing magic, learning the rules from a recent starter/duel kit and by playing arena online.

I just played against my friend for the first time, she is a huge magic fan and has been playing for at least 10 years. She was totally baffled when I tried to defend against her one attacking creature with two of my defending creatures. I explained that it was allowed, and that she got to choose the order in which her creature would fight my creatures. She said it must have been a recent rule change and that none of her MTG friends play like that. They always attack/block 1 creature vs 1 creature.

I believe her that it could have been a recent rule change, but I haven't been able to pinpoint if/when it happened by looking online. Anybody have any insights into when this rule was changed?