OKAY! I see some confusion on this last update so let me clear some things up!
During alex’s two last conversations with Hermione; she senses her soft spot for Draco.
On a whim, because of how nervous she was she writes to him, she’s scared for Mattheos safety and is desperate to reach someone who understands.
She realizes shortly after speaking to Draco that she found his soft spot… hermione.
She uses that against him to ensure someone will always be there to pull Mattheo back in if he goes too far.
Hope this helps! :)