Ash thought that her sister was lying about her financial destitution. Her only Feruchemical expenses were metal for her Nicrosilmind, not her addiction to oxygen or something more dangerous.
Ash left Scadrial, joining rogues Alene and drinking several oxygen bottles, which cost millions of spheres.
Meanwhile, Simon Kholin started embezzling Archbishop Tanner of millions of Breaths that belonged to Tanavast. He brought Ash the money, but she declined because she would betray Tanavast's trust later.