If she communicates well with others and just not with you,then she definitely is using silent treatment as a form of punishment.If she generally prefers silence, is not a talkative person,then it is just her personality.You said she holds grudges from the past.What had happened in the past?I mean she may be expecting some kind of closure.May be ask her directly why is she doing it?The silent treatment. If she is angry at something?She may open up and give you a chance at resolving it.
You mentioned being married for 40 years.Was she always like this through out the entire period?If this is a recent development, can you consider counseling?Is she going through menopause or depression? Plenty reasons to consider that bring changes in behaviours.