From my experience, the battle was simple, but hard to pull off. You see, I'm using (in my opinion, without sounding too selfish) best and well mixed Pokémon with each of their roles set in.
These are:
Slowking (Last Plot Kill) ; Krookadile (Anger Point Destroyer) ; Roserade (Toxic Spiker) ; Magnezone (Analytic Tank) ; Froslass (Destiny Bonder), and finally, my signature Pokémon:
Blaziken (Speed Bulking Blazekicker)
While I don't know much about your Pokémon moveset, I will, however, give you one strategy that I used on most of my Gym Battles whenever I cannot beat them with all-out attack.
The first Pokémon Emily sends out is that Eletric Bug pokemon. It only knows Bug Buzz, Sticky Web, Thunder Wave and Toxic. Pretty much status pokemon. Which pokemon you'll choose is up to you, as long as it can boost it's attack and speed (and probably defense against Bug Buzz to lower damage received). As much this sounds simple, it does relies on luck, since oppoment still can pull of crits, or even worse, switch out mid build up, and Ryker (the electric dog from Gen 3) will lower your Attack stat in case you were building physical destroyer, and might insta-kill you moment it ables to outspeed you.
So yeah, that's how I managed to pull off my win. You pretty much need to build your stats up including speed (Dragon Dance is what fits critically in the category, since it boosts both speed and attack), but feel free to create your own strategy, or take other suggestions, I did my job here.