She needs to know if these are not authentic. I stress "if" because I am too new to MK to say with certainty that they are fake, but my few months of infatuation with MK bags lead me to believe that they are fake.
However, it's difficult to imagine a situation in which you do not appear to be the bad guy. Because of this, I would first try to be indirect and not approach her directly about it. She has been your friend for 35 years and this would not seem to be the thing to cause an irreparable rift in that friendship. I love my authentic designer bags, but a friendship of that duration seems more important.
I would find/make a situation in which both he and she are present and you are all focused together (lunch/dinner at a restaurant) and she has the items with her. Gush over them to him and push him as to where he got them, because you would love to buy something similar for yourself/a friend/etc. Bottom line- I would try to put him on the spot when she is there and hopefully she will notice if he reacts oddly. If he doesn't give a definitive answer, I would follow up by looking online for the style with her present and perhaps you both can come to the realization "together" that they are fake after looking online and not likely finding this style to be an authentic one.
If this would not work, then I think you need to consider telling her that you suspect that they are not authentic. If it were me, I would want to know. It also makes me wonder about the future of the relationship if he is knowingly passing off fakes to her as authentic. That's a big IF, but it seems a red flag to me. However, this runs the risk of her viewing you as the bad guy.
I believe I've now completely overanalyzed this situation. I wish you the best in helping your friend!