I think you are right--I hadn't thought about a mummy, but this individual was fairly close to this colony, which I have tentatively ID'd as Tinocallis:
https://www.inaturalist.org/observations/92257591.

I'm trying to zoom in on that dorsal shot but the picture gets a little fuzzy. The way to tell is the setae. On abdominal segments III, V, and VII they are farther apart than I, II, IV and VI.

Here is an easy to see example:


The dots are the bases of the setae, so you can see how some have wider spacing than others. The big pair near the head are on the mesothorax, then the next three pairs are the metathorax and abdominal segments I and II, then III is the first widely spaced pair.

Your alate specimen has pretty distinct white spots but they're missing on III and V so I bet if I had it under a scope the setae on those segments would be farther apart. This mummy also looks like that spacing is there, it's just tougher to see since they're all black.

it appears that elongate black mummies are the work of wasps in the family Aphelinidae.