RUSURE - I have been to Lamanai, Altun Ha and a cave tubing trip. Altun Ha is a small ruin your wife should manage that quite well. Lamanai is a great trip - a long day but mixed with boat (or airplane), bus and more boats before you walk around the ruins. In my book, it's the best of the three tours you are considering. Cave Tubing requires a long walk, on uneven ground, carrying inner tubes and can be strenuous - not sure it would be the best thing for your wife.
I will add that when I did these trips, I was 100+ pounds overweight and have had back surgery. I struggled with the cave tubing but managed the Ruin trips. Happily, I am 100+ pounds lighter now and look forward to exploring the ruins again, but due to my back problems, I will likely not go cave tubing ever again.
I have not had the privaledge to join Tulu on any of his trips but perhaps I will have the opportunity during my trip to AC from August 12- 17!
Good Luck and have a wonderful time!