The Jenny Everywhere character concept was dedicated to the public domain (1, 2, 3, 4, 5), with the explicit intention that she can appear in any work under any license. Similarly to, say, Thor or Sherlock Holmes. (And unlike trademarked and copyright-restricted characters like Mickey Mouse or Superman.)
The Jenny Everywhere Paragraph is not a legal notice. "Longer works involving Jenny are encouraged to include this paragraph", one might even say strongly encouraged, but this is not a legal requirement.
If you make (for example) a copyright-restricted work featuring Jenny, you should include The Paragraph but you are not legally obliged to. If you include it, you retain your copyright and the character concept remains in the public domain. If you don't include it, you still retain your copyright and the character concept still remains in the public domain. But you don't get invited to parties.
If you are including or adapting other works (that Jenny happens to appear in), then you should always mention and abide by the license details of those other works, as normal.
If you want/need to formally recognise her inclusion the relevant fields would be:
Title: Jenny Everywhere
Author: Various authors
License: Public domain
Optional text: "The character of Jenny Everywhere is available..."
...formatted appropriately for your context.
Here is an example of an unchallenged appearance in a BY-SA work about six years after the first wave of "Jennymania". Note that The Paragraph does not appear:
Reality or bust! by Diana Nock. Licensed under CC BY-SA 3.0 US.