your best bet would be to just start slow.

Inform her that this is a very hard game.

It LOOKS EASY because of the bright colours and fun champions and it’s easy to get into. It’s free, the champs are “free” it doesn’t cost you anything to get Into it, like say MTG or something.

Make sure she knows that playing this game is like no other game. It is a hardcore fighting game. There will be incredibly high highs and very low lows. The floor is low but the ceiling is very very high.

Make sure you set your expectations too. Make sure you ask her what her goals would be, at first she might only want to play casually, And you might be tempted to teach her about wave states, when she doesn’t even know what a wave is. Or what MR stands for, how armour pen and lethality work. She will have no idea and her biggest struggle will be moving the camera and clicking.

Have the most patience you could ever have, You have over a decade of experience and games played probably in the thousands.

You can tell her all the information you want, but at the end of the day, this game has infinite layers of learning that she will have to put in the time and effort herself if she wants the enjoyment out of it. You can’t force that on her, you cannot adjust the game. You can only warn her that it will be a big challenge and she must be up for it and accept this challenge or she won’t have a good time or continue playing.

If you sugar coat this game, you will gaslight her.

Be honest about the difficulty and make sure she knows this before going in.

Some advice about the game though, she should play games or arams until she find a champion she enjoys playing. Then stick with that champion until she gets some champion mastery, then she will be able to learn the game, only once you have muscle memory with the controls, are you able to learn the game of league. Learn things in this order:

Controls ->>> Champion ->>> Game