Unlike Pokemon Sun & Moon, Olivia has actually become a little easier to defeat in Pokemon Ultra Sun & Ultra Moon. That being said, however, you can still easily lose if you being to underestimate her. To make sure that doesn't happen, simply bring a few Water Type and Steel Type Pokemon into battle against her. Most of her Pokemon are extremely vulnerable to Water Type Attacks, but all three are also quite weak against Steel Type Attacks. Believe it or not, the Hawlucha you can trade for in the Route 2 Pokemon Center can also help you with Kahuna Olivia, as its Fighting Type Attacks crush both Lileep and Lycanroc.