I know I'm probably the ONLY person in the WORLD to say this, but Titania was the easiest gym leader of all 16 leaders for me. As to answer your query:
I would suggest you head back to tourmaline desert and catch a dugtrio (Yes I would prefer using dugtrio over golurk or excadrill because then you'll always outspeed) and use dugtrio to one shot her excadrill and klefki. And as for her aegislash, you can easily one shot her using sucker punch from absol (Also when using sucker punch, you don't have to deal with the king shield attack drops as sucker punch will fail if aegislash uses king shield thus you will not make contact and you don't have to deal with shadow sneak as sucker punch has priority. So Sucker Punch is the best option) As for Absol, I caught it at route 3 below Calcenon City.
