Thank you note to ex-aunt who wasn't invited

So, this is very much on me, and I need some help with trying to overcome this faux pas. My aunt and uncle separated in the last two years. I invited my uncle and their two kids (my cousins) to the wedding...but didn't invite her. We aren't close at all (I have only been around her/met her a handful of times because they lived abroad for most of their marriage) and I let that and their separation sway me away from inviting her (I'm pretty sure she wouldn't have been able to come anyway, but that's not the point). It was clearly a dumb move, but I can't change it now. She sent us a brief but sweet card and a check. We of course will be sending her a thank you note, but my question is whether (and how, if so) to address the lack of invitation. I feel like my options are either to address that and apologize or just completely ignore that whole fiasco and just say thank you and hope you're well. Anyone have advice for this awkardness?