HI there I will try and help
the deed of trust is a perfectly adequate way of protecting an interest in the property. This protects your "beneficial interest" in the property which basically means the equity in the property. The deed ensures means that as a trustee protecting your joint interest she has certain obligations on sale of the property to distribute the equity in the way the deed dictates.
This however doesn't stop any changes to the "legal" estate. So she could, if she wanted, put a new or second charge could be placed against the property and potentially eat into the equity.
Therefore to ensure that you are notified of any potential dealings to the property you could agree to register something called a "Agreed Notice" against the property. This form can be found on the land registry website and the details of how to register