If they're an absolute theme park beginner, I'd start with one of the water rides. It's just one (relatively) small drop and it gives people confidence that they're not going to freak out or puke or die. Water seems to sooth most people too. Maybe it's the idea in the back of their heads the water will break your fall or something.
As far as rollercoasters, I'd say the Scorpion is good for beginners. There's only one small loop and the first hill is around 60 feet. It's a short ride, and very smooth. I really like this coaster, it's a classic, which is why it's still there and older so-so coasters like the Python have been removed. The scariest part is probably the "head-choppers" where you zip close to the support poles. Most riders involuntarily duck.
You can also see the whole thing before you ride, that helps some people. They aren't imagining 500 foot loops hidden somewhere along the track. There's usually lots of smaller kids in line since the height restriction is about a foot less than Kumba. Your friend might have enough self-respect to not chicken out in front of a 7 year old, lol.
The Sand Serpent is nearby (used to be "Cheetah Chase," not to be confused with the new "Cheetah Hunt.") But believe it or not it scares some people more than Kumba or SheiKra, even though it doesn't look like much. It's also kinda rough when you take those corners.
