Speak to her yourself, Ghost!
You clearly have the power of speech.
Why you getting’ all shy in your ethereal years? You’re not showing yourself either. Even if you have some weird clause in your death contract about only speaking to your son, you don’t seem to have a limitation on who you can show yourself to.
I mean, Barnardo gets to see you, for crying out loud. But you can’t make a ghostly appearance to your wife? Who you loved? Who is clearly thinking that her son has lost his mind?
The rules of being a ghost are very confusing.