What I want you to do is bring Equin0x to a computer and show him the following videos:
https://www.youtube.com/watch?v=d5VEREaXscw
https://www.youtube.com/watch?v=cpgYVgkXT9o
https://www.youtube.com/watch?v=2t0_9PFQPwM
After that, hand him a controller and ask him to perform any of the combos shown in the videos. If she's so braindead then he should be able to complete them, no sweat.
In all seriousness though, he should honestly be able to understand the difficulties involved with playing Sheik if he's actually a decent player. Sheik is undoubtedly the best character, with the most amount of options out of the whole cast. This is a double-edged sword however. Having such a large array of options means there's an intense understanding of the character needed in order to understand where and when to use them. Sure, anyone can get off a few F-air strings in a match. Not everyone, however, is able distinguish the drastically different games Sheik must play when fighting a Lucario, or a Rosalina. Would Equin0x be able to tell me when F-air > Bouncing Fish starts working? Or perhaps he'd know what the point of ledge flipping with down-b is? Unless he's studied the character himself, I highly doubt it.
If you need some additional ammo, here's Seagull Joe, the player that beat ZeRo, saying that Sheik is the
4th most technical character out of a cast of
55:
https://twitter.com/SeagullJoeSSB/status/652853186231988224
That's got to count for something.
All that being said, you're friend sounds hella salty.