Sister O'Reilly is probably dead. One of the main reasons for setting up a trust like this is to avoid inheritance taxes. Older rich people set them up to make sure their money ends up with somebody they want to have it.
Some basics about trusts. A trust is its own legal entity, it has its own tax ID number and its own registrations with state and local agencies. There are three main people (or other legal entities) involved in it.
The Grantor (in this case Mrs. O'Reilly) has her lawyer write up the appropriate legal paperwork to establish the separate legal entity. Those documents designate a trustee to manage the affairs of the trust. That person cannot be the Grantor or the Beneficiary. The Beneficiary receives the income generated by the assets in the trust. All legal power to manage the affairs of the trust reside with the Trustee, the Beneficiary can't tell the Trustee to do. (Neither can the Grantor after the trust is set up and funded). There are sound legal and ethical reasons to do this. If your son is an addict you might write trust documents that tell the Trustee to make sure he has a place to live and food, but not to give him cash because he'll buy drugs with it.
The trustee has a legal duty to do what the trust documents tell him to do. I know the WTBS has a brochure about leaving your money to them, I'd love to see a copy of it if anybody (Blondie?) can tell me where to find it. I suspect that they have this all pretty well spelled out in their "suggestions."
In this case the trust documents probably tell the Trustee to do the best he can to maximize profits, and therefore income to the Beneficiary (the WTBS). Including details about how to invest money might well create a legal conflict for the Trustee, and would have been avoided by whoever wrote the trust documents. Assuming he knew what he was doing.