Playing worse against lower-rated players

I have a family-friend that is obsessed with chess, and would love to get better, and plays all the time, and they said they would love to take private lessons from me, and improve. I’m rated 1800 online, ( I don’t play on this account) and they’re rated 1000. So I should be able to beat them 95-99% of the time. But guess what? I lose to them all ALMOST HALF OF THE TIME. And this is in daily games, believe it or not, where I have all the time to think in the world. When I started playing with them, they claimed that I’m way stronger than them, but clearly I’m not. At the end of this month, or maybe sometime next month, if not, pretty soon, I’m going to meet them in real life, and see about taking lessons with me, and so far as I’ve played them online, I’ve had terrible showings. What’s the point of them taking lessons with me if I get destroyed half of the time by people nearly a thousand rating below me? Any suggestions what/how to study?