What should I do to enable them normally?
Honestly, fuck if I know. They should always be enabled, the problem is that there's always some other line that takes priority. You might get lucky and her very first action during an encounter will be using dirty talk, and then *maybe* she'd use one of those lines... but probably not.
The way the system seems to work, from what I've seen digging through the source in the past, is that there's a default pool of 'dirty talk' lines (there's actually a bunch of pools, but whatever). The character class apparently has unique lines that it can interject as well, which is what you're seeing. When dirty talk is used, it selects a random line from the appropriate pool.
However, those lines can be completely overruled in a number of ways. Passive stats (like lust, or active fetishes) or specific actions (tease responses and ongoing actions) have the ability to override the selected pool. And then on top of all that there's state based stuff that override whatever options make it to the top. If you have something in your mouth, for example, whatever line was going to play is just dropped and replaced with some muffled sounding text.
It might be impossible to ever actually trigger those lines, simply because there's so many layers to the system that they'll never be selected.
Edit:
Anyone out there still watching the discord? We're on 10 days with no update or word, not that I'm expecting much. Is Inno actually talking in discord like usual?