I have a dilemma!

I have a dilemma.  I'll try to write this so it's easy to understand.  I'd like your opinion, please.

• I have a fairly new neighbor, Lady A, right next door.  She moved in about a year ago.  She's around 90 years old and active.  She's a retired nurse, and served in WWII.  She walks a couple of miles every day.  She's very friendly, but she's not friendly to Bob or I.  She even came to my Tai Chi class for over 6 months and avoided talking to either of us.
• Lady A, really likes men.  If you see her talking to someone, while she's out and about, 80% of the time it's a male.  I also like men and don't think it's a character flaw.
• At Easter, this year, Lady A, left Easter cards on doorsteps of men, signed Love, Lady A.  If the men were married, the cards were only addressed to the man.
• We have some friends, Mr. and Mrs. B, also neighbors, who are part of our card-playing group.  They've been married over 30 years, this is the 2nd marriage for both of them.  He's 86 and she's 76.
• Mr. B, like my Bob, is the chief dog walker for their family.  He walks their dog once in the morning and also in the early evening.
• Mr. B received one of the Easter cards.  Mrs. B wasn't very happy about it, but choose to ignore it.  Mr. B just shrugged.  (Bob and I both thought it was inappropriate and speculated that perhaps it was an early sign of dementia, on Lady A's part.)

• About 3 months ago, I was out in the early evening delivering flyers.  (It's one of my volunteer gigs, if the HOA Board thinks info. needs to be quickly disseminated, the volunteers get in gear and deliver the info.)  I walked up Lady A's sidewalk, right behind Mr. B.  She greeted him at the door, "Well, hello sweetheart."  He and the dog went inside.  I gave her the flyer, and went on with my rounds.  I mentioned it to Bob and we just shook our heads.
• Fast forward to about a week ago, I went out the front door to collect the mail.  Who should I see walking up to Lady A's door, and ringing the door bell?  Mr. B, of course.  I greeted him, and went to the mailbox and Mr. B and the dog, went into Lady A's.
• When I was back in the house, I told Bob, "Mr. B is at it again."  Bob said that when he walks our Dudley in the evening, he frequently sees Mr. B make a beeline for Lady A's!
• Since I've observed this twice, I'm very uncomfortable not saying anything to Mrs. B.

To me, it's entirely acceptable to encounter someone and stop and chat; but it's an entirely different matter to do something premeditated.  Walking up the sidewalk, ringing the bell, entering the house, is premeditated, not casual.  That's my dilemma, should I say anything.  If so, what should I say.  I think not saying anything leaves me somehow complicit.  I think these are my choices

1. Say nothing, since I'm not affected.  Plus, I speculate saying something would change our card group.
2. Tell Mrs. B that I think she should walk the dog with Mr. B in the evening.
3. Tell Mrs. B what I've observed.
4. Tell Mrs. B, in front of Mr. B, what I've observed.

I know that if I were Mrs. B, I'd want to know.  I don't know what Mrs. B would want.  I don't think there's an easy solution.  What would you do?

Thanks for stopping by and sharing my life with me,