Trust the Psi Corps.
You are not evil.
The trust idea is good in principle, but easy to get around. Being an "ex-financial genius" myself, here is how you get the cash right away:
Say I want to get $50K of her money before 2pm thursday. I call a wealthy Scilon and brief them on the sit. I get the sisters agreement to do the cycle for $50K. I introduce the wealth Scilon to your sister and they- independently of me (even though I set it all up)- decide that the wealthy Scilon will lend the sister $50K (which she gives to the org), and she will pay back the said wealthy Scilon at say, oh I dont know, maybe, $1000 per month? for the next 5 years or so. KA CHING! I am now upstat and get libs this weekend, and your sister continues to live in poverty.
The same thing can possibly be done with a bank for financial institution if you can prove the money is coming in every month and that it is a sure thing, but you will get less money loaned that way.
Its a dirty business I am afraid, you'll have to get smarter than that if you want to help your sister. You are better off with the lifetime medical or something like that, something that cant be cashed in or sold or have the ownership transferred. If the lifetime medical could be transferred in ownership, then you have the possibility in kind, in exchange for cash, similar to the situation I outline above.
Yours is exactly the reason I outlaid: modest rent (direct to landlord), weekly food supply (if such a company exists in your country), Medical cover, and watching the bills.
From the outside it looks like treating the sister as an "incompetent" but, as I pointed out, if the Will sets the Trust up properly (citing other cases of church-induced poverty), even Judge Judy would tell the Church to F off.
If such actions damage the surface relationship with the sister, then so be it. As pointed out above, if/when she wakes up, she will be grateful.
A reg cycle fo $5000 is going to look a bit silly if it has to be paid off at $5.00 per week.