I am looking at the newer model Discoveries 2018-19 for my wife. Are they any better maintenance and reliability wise when compared to older models?
Let's make sure we are addressing the correct vehicle - are you talking about the Discovery Sport, or the L462 Discovery 5? They are completely different vehicles.
The Disco Sport is not much more than a typical small luxury crossover that is fine for light off-roading on forest roads. The Ingenium gassers are doing fine it seems, but the Diesel 4cyl Ingeniums are indeed highway drivers - you will require more frequent oil changes if you daily drive them on short trips around town. But just buy a vacuum pump and do it at home, and avoid the $150 dealer charge, or buy prepaid maintenance if it's a new one.
The L462 D5 is a true 4x4 designed for hard off-road use. I have a Td6, and it's a dream. Same basic engine as the Ford F150 Powerstroke diesel - in fact, Ford designed it and builds it for Land Rover. In the F150 they beefed up some components to give it the 10,500lb tow rating but in the D5 it's good for 7700lb, emissions-limited. Mine has been trouble-free for 32,000 miles so far. A set of AT tires and it's good to go on the vast majority of offroad tracks and trails you'll ever encounter. Look for one with Terrain Response 2 if you're buying used. You can also get a rear locker but then you have to buy the 3-row version and sacrifice some cargo space.
Bottom line, Land Rover has improved light years in terms of reliability - but they still generally rank lower than other brands. The Range Rover Sport did beat Acura MDX and Audi Q7 in 3-year dependability (2014-2017) in its first model year of the new generation in JD Power assessments (put whatever stock in that you wish but that's owner reported), and that's the same platform and running gear as the Discovery.