No softlock, you just didn’t read properly or didn’t try to bruteforce it hard enough.
The diary is for Dhena.
Emmet said that he sprayed the tree with pesticide recently.
Erica said she was reading under the tree.
Use Emmet’s evidence against her.
Then she’ll give you evidence you can use against someone else.
And once again, that someone will give you evidence for yet another person.
No softlock.