In those circumstances there must be a strong inference that she is a constructive trustee of the bonds. She has used trust funds to subscribe for the bonds. Equity would not permit her to hold them otherwise than on the existing Will trusts. If she is the sole trustee an assignment is somewhat over the top. Although you can assign to yourself in a different capacity here she would be a trustee on both sides, constructive as assignor and appointed as assignee. I suggest all she needs is to receive positive legal advice that she needs to do nothing and why. Even appointing a co-trustee just for a meaningful assignment seems excessive if the Will trust is not one of land and if is not considered desirable otherwise e.g. to secure trusteeship succession.
Jack Harper