If you're looking for an addition to your team, Klink can be very effective against her. Additionally, if you have a Poke with high happiness, you can go the western-most building in the Obsidia Ward and talk with a woman near a Vulpix. After a short side-quest, the Vulpix can join your party. Vulpix is fantastic against Shelly, because once it uses Flame Burst, the field becomes the Burning Field effect.
I would recommend adding Klink and Vulpix to your team. And again, use Hariyama. Train that up a bit and get it in use.