Although she's from the future, it's from an alternate future. The 'canon'Danny won't become Dark Danny. At least, it's what I know about that episode
That's right. That future was from when Danny cheated, but Clockwork got involved to prevent that from happening because of the Observants telling him to. Depending on whether there's a multiverse or not, that future timeline might not exist anymore. Clockwork is the master of time and knows everything that can/will happen.
Clockwork: "The Observants look at time like they're watching a parade, one thing after another passing by in sequence right in front of them. I see the parade from above, all the twists and turns it might, or might not, take."
Danny: "You knew all of this was going to happen, all of it, even this part."
Honestly, Clockwork should be one of, if not the strongest ghosts in the Ghost Zone. He probably just doesn't get involved in anything unless it's world destroying or something and only he can handle it (like preventing Danny from being Dan/Dark Danny).
Anyways, my point was that in that timeline there were (likely, unless it was the other option I stated) ghosts that had a kid. If there were ghosts that had a kid in the timeline where Danny cheated, it should be possible in his timeline as well. So, ghosts should be able to get pregnant in the game.