This is more or less what I was feeling when advising not to do or say anything malicious at this stage op. I say that with the proviso that, as I understand it, you now have the money back? ( Though have you confirmed this with your own eyes!?)
You were asking me why I felt the anger was justified before, but it is time to ease down. I totally understand why you are angry - and as another op pointed out it is still very fresh.
However, up until this point your anger was directed at achieving a purpose, namely restoring the funds to you. This was a reasonable demand and needed to happen. Until it hadn’t been rectified, anger was a justified position. However, people have to be able to put things right and, as I understand it, she has. I wouldn’t be trusting her again, I’d be very clear with DH that you are opposed to any further financial involvement with her. But all those things are designed to give you substantive protection. Going to the party and publicly humiliating or “ outing” her is just vindictive at this point; it can’t bring about further restorative action on her part, but merely seeks to upset her, which will backfire and make you look ( and ultimately feel) like the toxic one. If she’s given it back, she can simply say that and any third party would - with reason - wonder why you are ruining the evening for everyone about something that is already rectified in substantive terms.
I can see it might have been cathartic to have a grovelling apology, but I’m actually not sure your DH has been open enough with her about the background on your side for her to understand you might expect one. It seems to me he has fudged and concealed your objections with stories about his sister needing it back etc etc. I don’t think the woman has the full picture because your DH has obfuscated, trying to look (I think) like the “ cool headed financier.” I understand that was wrong of him, but you have to be careful to isolate the strands of the situation and see what aspects she is actually responsible for.
MN can be a place where, because there are women seeking to empower each other, ( which is great) there can be a subtle digression from having your claws out justifiably to stand your ground, to a less discerning blanket attitude that being a “ fearless woman” who is generally hurling insults and baying for blood is some kind of role model to aspire to. I think it should be all about proportionality ( and I suspect sometimes the ones who claim “ I’d just be telling her, doing Y” are often playing out fantasies or simply wanting to escalate someone else’s situation for the juicy updates. LTB for all manner of minor transgressions like leaving up the loo seat is a classic eg of this!) .
Use your anger when you need it, but not to drag yourself down in a cycle of aggression and ill will. And bravo again for getting it back!