Implementing RTD or notification on an existing desktop app via Reflection

It is quite specific condition. We have 3rd party desktop (.Net) client application that accepts external dll files wrapped in certain namespaces and class names to allow write your own code on runtime inside the app.

What I need is that whenever a record is registered on table of a database (say User), I have to notify my app. (I need to push added user object to a list inside user.dll)

I dont't have much information about signalr and reflection, however, just on paper, I think of creating a signalr hub that listens database and notify my app via user dll.

Here I visualize the parts; I left middle question mark because I may not aware for a better solution except signalr.

By the way, I am also not aware how I am going to notify the app via user.dll, I think there will be problem here because my dll is just a class library, I may not hook events here.

I didn't know how to search this, or how to implement events in a dll file, so i decied to ask it here, any help or guidance will be appreciated.