Ash's Bayleef doesn't know a move that can counter a Fire/Psychic-type like Delphox or a Fairy-type like Sylveon.

>Razor Leaf
>Vine Whip
>Body Slam
>Headbutt

And yes, she can learn Iron Tail. It also looks like she isn't able to learn a move that can counter Pancham, unless you count Natural Gift, in which, if you have a specific berry, Nature Power can be either, flying, psychic or fairy-type which counters Pancham. She also doesn't know Ancient Power either which counters Delphox, which is a Rock-type move.

Sorry not sorry.