Yeah, Arrancar don't use any metal, have no metal too... they're all that special Hollow Bone stuff for their equipment. Not only that, but being dead spirits, I don't even think they have Real Elemental Metal in their blood and tissues. As such, Magneto's magnatism shouldn't really be a major problem for her, aside from having to dodge and parry thrown objects and smash through his shields. But Captains and Arrancar should have the strength and speed to pull it off, and Tia is the 3rd most powerful (now 1st) Arrancar in all of Bleach.