Tell her, in MC, that you feel that her keeping the love note from OM is disrespectful to your marriage, and that you need her to dispose of EVERYTHING that she has that has to do with him.
DMB, she is still CARRYING THIS AROUND WITH HER. That's just hurtful, and a good MC can show her how this is not only what YOU need right now, but it's also not helpful for her OWN healing.
So much for her using her time at the beach, and her "space" for any serious self-reflection. Intead, it's "Gidget Loves Tony" high-school b.s.!!