Athena, when it happened in my game it was long before Generations. The only thing I can remember about it was that I think someone in the household had travelled just before the problem occurred. It was in my Clan Douglas Immortal Dynasty, and it was more than half a year ago, so I'm afraid I can't be any more specific. There were a number of problems with that game file near the end of the dynasty, and I can't even say for sure that travel was a factor. If it helps any, I know that particular problem hasn't happened again in any of my other games, so it should be safe to restart if you want to.
To get the Culinary Librarian LTW, your Sim needs to know the number of recipes that are in the base game - I think it's 28. But if you have World Adventures, there are also 2 recipes from China, 4 from France, and 2 from Egypt. If your Sim is able to learn those 8 recipes on top of the ones she still knows, would that give you the 28? If not, I don't know what you can do other than restart your game, unfortunately.