I'm with what @BCsven@lemmy.ca said: get s mixed box if unsure.

That said: highly depending on her age and interests as well there is no need to go deeper into specific bricks.

After all the only thing that prevents a couple of 4x2 to become an airplane is imagination. Or a fire, a house, an animal.

So I suggest depending on age and interest to just talk with her and adjust accordingly.

And: especially Lego can be sometimes sniped used in big mixed boxes at flea markets and the likes - something that would bring s but of lootbox excitement in your lifes without the downsides;)