Unless one is intimate with the details of how Isabella conducted her financial affairs, it is guesswork at best to blame her relative lack of funds on an entire industry of people. Who precisely stole from her? She did hold down quite prestigious jobs, such as fashion director of the Sunday Times. If she mismanaged her money, that is not the fashion industry's fault. It is also economically nonsensical to say that, because she was so creative, she deserved to be handed money without doing anything to earn it; Knight writes as if society should have provided Isabella with a massive stipend for life, just for being born brilliant. (Isabella came from a very wealthy, aristocratic family, but was left with only £5000 - about $10,000 - as an inheritance. I have no idea how much she received outside of family wills.)
Also, let's keep some perspective here: How poor is someone, really, who has the lifestyle Isabella enjoyed? As if having to pay Alexander McQueen in weekly installments of £100 for his entire graduate collection is something over which we should gasp and weep.
As for blaming her death on the fashion industry, that makes as much sense as blaming the suicides of countless writers, actors, and comedians on their respective industries. Yes, you take knocks in those businesses, but find me a way of earning your crust which doesn't impart some hardships along the way. It's a cliché to say this, but that's life. Isabella did not need the whole of the fashion industry to descend upon her in the Priory, but the few close friends on whom she could count. She had them, and mental illness. Poor thing.