Bench Primarina for this one, replace Kricketune. You should have access to Meowstic by this point, who is a very good option for this fight, both Female and Male version. If you're willing to train up a mon, you can get Pinecos from the Headbuttable in Reborn City trees for a Forretress, who invalidates a lot of Aya's team, knows spikes(which is boosted), and has attacks independent of it's attack power. (Heavy Slam/Gyro Ball). I can't really stress how good Steel types are against Aya, as she only has a handful of answers to them. If the egg you got from the Slums was Bronzor all the better.