See activities without following

This is more out of curiosity than anything else. I follow someone who doesn't follow me back. In fact, she follows very few people. However, she regularly gives kudos on almost every workout I do, usually within a couple of hours, and I've seen she does the same for others she doesn't follow as well. I can't imagine she's sitting there manually typing in people's names throughout the day to see who has done an activity. So how does she know when someone she doesn't follow has posted an activity?