You can use a save editor and verify that the "ClawynPregnancy" variable is actually advancing over time. If you don't think that it is or if you just want to get her back then you can set it so that the scene will trigger and then she can rejoin the party.
The easiest is probably to go to:
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Check variable #1014, then go around and do "something" (visit a few different cities, complete a quest or two, sleep at the castle or an inn, ....), then save again and check that to see if the number has increased. If it hasn't changed at all then it may be stuck and not updating. You could also just go and change it to >18 and the scene should trigger.
Another editor is RpgMakerSaveEdit.exe which also allows editing of the save files.
If you are really stuck and can't seem to get her back in the party I can check your save file for you if you post it.