It has not been patched. Generally I'd suggest watching and comparing your attempts to those on the leaderboards to figure out where you did things differently. Nonetheless, here are some things you might wanna look out for when performing the trick.

Does she immediately turn around after you've thrown all your ash and used all your snapseeds? If so, you cut the corner early and aggroed her - making a aerial stealth deathblow impossible.

If she doesn't turn around even after you've used all your items - Do you properly put your characters back against the gravestone, jump straight up, and then jump off of the stone straight to the front? Reaching a certain height is important. If you don't reach a certain height, the deathblow-marker won't appear. (Though with 8ash (assuming all connect and slightly push her back) it should be fairly easy to reach the needed height even with a not-so-clean jump)

Feel free to join the Sekiro Speedrunning Discord Server for help regarding anything about Speedrunning Sekiro: https://discord.com/invite/ZuXAVEx