When I log in as admin and search Discourse settings for controls like level 0 or reply frequency or post rate, I don’t see anything relevant.
If I google discourse level 0 to learn what it means, I see this official blog post. It doesn’t appear to limit how quickly a user can reply. And it appears to prevent other features that aren’t a problem (that we yet know), such as preventing DMs.
The problem is we have a user who replies to every reply in many threads as soon as she gets a notification email. It might be helpful to prevent her from replying to a single thread more than X times per day. The goal would be to keep her from writing in anger, and to let others get a chance to reply before she replies again.