This was a pretty good one.
I liked the character's design, the arrangement, and for the page limit, they did a good job establishing that Count as the antagonist.
The rehabilitation of the prince didn't feel that cheap, and it didn't feel like they were making him overtly pathetic to sell it either.
This could have just been a normal reincarnation story without the villainess angle and in fact could be a tighter story for it, but I guess throwing in some hooks to get eyes on the story isn't bad. She certainly proved herself a skilled schemer at the end too, despite fucking up the lie almost immediately.
With this pacing, even if this were serialized, I imagine it would only be like 10 chapters long with some extra scenes packed in so that we're shown instead of told details. Even then, the final product might not measure up to this oneshot.
Anyways, this was well done enough that if someone told me this author wrote something else, I'd be interested in checking it out.