I don't think the Thais really care that much, one way or the other, BB -- not like we in the West do. People go on and on about "face" in this part of the world, when we have the same thing, it just works differently in the West. While in many ways Thais look at anyone who isn't Thai as a barbarian, at the same time, they don't hold us to the standards they hold other Thais to, simply because we aren't Thai.
On one hand, they are amazed that falang would be so brazen as to be stepping out with a working girl in public, something a Thai man would never do (if you've ever seen a Thai brothel that caters to Thai men -- well, you haven't because unless you knew it for what it was, it would look just like another house, office building, etc.). The fact that it might be a lady, ladyboy, or some twink boy from Boystown you're walking with is immaterial. But then it's not a loss of face, per se, because we're not Thai.
Much less stigma for us here, doing that, than back home, to be sure -- even if you are public with your preferences -- unless of course, you live in a place like San Francisco or something. Even then you may run into some asshole that feels justified in verbalizing his or her opinion of you.
To be honest, I think Thais are more scandalized by the fact that guys will walk around with shorts on at a nice restaurant, or walk around on the street with their shirts off, than anything else. Evidence of our barbarianism, 555. Seriously, ask your lady about this sometime, if you haven't already.
I just waltzed down my soi earlier this afternoon with Miss Fah in tow, in her work clothes and fuck-me high heels, because we forgot to stop by her place to pick up some street clothes once we got in the taxi last night. Most of my neighbors were out; I said "sawasdee" to the ones I normally chat with, and did even stop to talk briefly with the lady I buy food from sometimes. Hardly anyone batted an eye at Fah. There were a few second glances, but no snickers or rubbernecking. And I can catch enough Thai now to know when I'm being discussed.
Granted, maybe they just waited 'til I was out of eyeshot/earshot, but when I walked back home an hour later by myself, again, it was business as usual -- no knowing grins, or anything like that. And it's not like I make a habit of this; in the six months I've lived here, she's only the second lady I've brought home (as you know, I tend to save the whoring for the weekends down in Patts).
With regard to your old lady, that makes all the difference in the world when the family will pony up for an education -- an uncommon thing for a rural family to do. She would have had considerably fewer options if she wanted to get off the farm/out of the village with an education. But then that's the same the world over, to one degree or another. Good on her mum.