From the start of the game, choose these options in the dialogue with her.
Maybe it’s a good idea! → You don't have to do this to yourself, you know... → Corruption path
-or-
Uh... isn’t that kind of sexual profession? → You don't have to do this to yourself, you know... → Corruption path
Yasuka’s corruption path was indeed added with version 0.6. So if you did download the 0.5.9, it would be normal for you to not have this content :) You can head to your purchase and download the 0.6.91 from there :)