What does the "(Land Registry)" bit mean? You don't need to do anything at the Land Registry to create a trust of land as far as I know (a trust can [and in some cases, must] be entered as a restriction on the register but whether it is or not does not affect its validity). The only formality to create an express of trust of land is that in s 53(1)(b) LPA 1925.
If you think this is an express declaration of trust by Abigail then constitution doesn't come into it. Constitution would be relevant if she was passing legal title to someone else to act as trustee: "Fred to hold on trust for me and Edwina". As she already holds legal title she doesn't need to constitute anything.