Answer

Greetings.
First of all, from your description she did deserve a rebuke. But public humiliation is indeed a problematic thing. Especially the reference to modesty, which seemingly tells the people listening that modesty is unimportant. Let me begin by saying that it is admirable that you are looking for a way to repent, and clearly there is nothing for you to do beyond making a sincere effort. So do not let your heart fall.
I do not see a practical solution for reaching her, and so it seems to me, by reasoning, that this is like a thief who does not know to whom to return what he stole (he cannot locate the victim). In such a case, Jewish law says (Shulchan Arukh, Choshen Mishpat, sec. 366 and elsewhere) that he should give the money to public needs, and of course in the background there is the possibility that perhaps the victim himself will also benefit from it somehow. See, for example, the discussion here:
https://www.yeshiva.org.il/midrash/16210
True, in your case this is not actual theft, so at first glance it is only an external analogy. Still, perhaps one can learn from here that you should do things to prevent people from being humiliated (study the topic of humiliation in Jewish law, and afterward give a lecture and/or write an article on the subject).
On second thought, I realized that humiliation is also a kind of damage for which one pays compensation (damages for humiliation), and so there is room to compare this completely to theft where one does not know to whom to return it. If so, then one may pay the humiliation compensation to public needs.
There remains the question of assessment: how much are the damages for humiliation of such a woman? In Bava Kamma 86a, Rashi explains that this is the amount that that person (the one being humiliated) would be willing to pay in order to spare himself that humiliation. I think the estimate of that is entrusted to you no less than to me.
Bottom line: estimate how much a woman like her would be willing to pay to spare herself such humiliation (you can do a short survey among your wife’s friends). If you also write an article or give a lecture on the topic of humiliation and repentance for it, it will certainly help bring atonement. If you would like, I would be happy to help you with this. Perhaps if you and your wife write the article together, we can publish it in the Midrasha journal “Derisha.”
And again, do not lose heart. Your intention was good, and anyone can stumble in this, especially when there is a justified trigger.
Regards to your wife as well (has she already finished?), and all the best,