Sorry to hear the frustration and unconfortable situation you were put through. I am not saying I agree, but I acknowlege that there is alot of dissapointment, discomfort, and overall lack of satisfaction expressed in the tone of your post with the situation.
However, I would like to just comment on some things that differ in my oppinion than yours and to acknowlegs some items that I agree with:
1. It is true that there was a lack of communication and you may have been put in a situation of believing that your "wife was going to be taken care of one-on-one". Now you know for next time, albeit, you found out the hard way.
2. But with a big boat, leading a large group, "Dawn" has a valid point that she has to rely on your wife and her training.
3. I diagree that all individuals of a group comprised of a varied aray of experience needs to head up with the divemaster.
4. "Dawn" should not have made assurances (if she in fact misled you) that she would "take care of (babysit) your wife" while knowing darn well that she would keep her down with the rest of the group and not be able to focus on the appropriate, non-loligagged ascent for a low on air point of the dive.
5. 700 psig is not necessarily a totally bad thing at 85 feet. It varies with individuals (within reason and air management and consumption calculations, etc., etc.) . Now you and your wife know what your comfort level is and that, as is typical of new divers, your wife is now an air-hog (which will improve over time and experiance). Set a limit of 1,000 psig to start the ascent from 85 feet and a turn around psig of 2,000 psig...or whatever is appropriate for your comfoprt level.
6. Rack this one up to simply, "Is "Dawn" and her livaboard going to get your repeat business any time soon. I guess you rectified the sitaution already with the amount of your tip and whatever decision you have already made about giving repeat business. I doubt you will get a sorry, or financial amends in the form of a discount on your next trip. Just not going to happen. Get over it, and like you have already done, make sure you are asking questions from a learning perspective as opposed to a jab at the reputation of the business. However, it sounds as if you had received a "sorry, we will dio a better job", then you would have been a little more closer to being happier?
7. You have over 20 years of diving experience. Why the hell did you not brief your wife and buddy up with her and take care of her, as opposed to expecting "Dawn" to do it for you?
8. From a learning perspective, if that is the whole point of this post, it is classy to leave out the name of the business. Otherwise, the post reaks of trying to harm or discredit the business, and the "learning" point claimed loses all credibility to a whine or complaint post.
9. Nitrox and no-deco do not sound like they were a factor in this situation. This situation appears to be purely an air consumption situation.
Anyways, sorry about the miscommuncication. It sounds like you know better for next time.