Being childless and already targeted by multiple plots to put someone with a plausible claim in her place, Elizabeth was SERIOUS about not allowing marriage without her say in the matter. Even idle discussion about succession at court or elsewhere was a great way to get questioned or worse
It's also notable that diaries are glaringly absent in this period and personal correspondence was often burned as a basic precaution. You really didn't want Walsingham reading your candid thoughts on paper.
I recall reading an excerpt from a surviving letter of a father to his son who was a junior officer under Essex in the 1599 campaign in Ireland. He advised his son to say nothing of his opinions to anybody and keep his ears open above all else "Essex hath friends. He hath enemies also"