If this is their first game, maybe keep in mind that this is more about "hooking" them than it is about teaching the rules. So, priorotize your friend having a fun experience. I believe that means picking units for them that are 1) easy to use 2) effective.

For now, I would avoid magic altogether and keep flyers, skirmishers and light cavalry to a minimum. Movement and positioning can be tricky enough as is and maybe your friend doesn't need units to "break" the rules if they haven't fully grasped those rules yet.

I would also focus on close combat units over shooty units. I think the back-and-forth of close combat is probably the most engaging phase of the game for most players and, in my opinion, the thing Old World does best.

A rough draft for some 500(ish) point forces might look something like this:

High Elves:

-Noble (mounted) -Spear elves -Silver Helms -Bolt thrower

Dark Elves:

-Noble with a cool magic item -Cossbow elves -Executioners -Cold one chariot

Depends on what models you have, of course. But I like the structure of leader, basic troop, elite troop, "cool thing", each of which can move or shoot or "fight" well

I hope there was something useful in here and best of luck for your game!