If he really wanted to destroy them, he would have done so.
How can they do any damage now?
My db is currently transcribing, the almost illegible, letters between our parents when they were separated for long periods during the 2nd world war. They are innocent, a bit soppy, and it would be sad to destroy them.
I am also reading some early 19th century letters between husband and wife, who lived in the house I now live in.
It is a privilege.
Lots of affectionate chat about the children's behaviour, ailments including worms, travel, comments about local characters, money worries and daily life in general.
They had 11 children so there was plenty to talk about.
I am donating the letters to our local history society.
You must tell your friend to read hers before she can arrive at a decision and then she will know what to do.