Same problem, I have UFO as well. I have tried dismissing all followers but one. I have tried dismissing all followers and brought an entirely new follower. Have tried uninstalling (completely). Still results in her saying "I will give the oath to such and such" but she never does. For what it's worth I also have Paarthurnax Dilemma and Just More Blades mods, but from what I understand, the problem seems to be with UFO. Any inputs on the matter would be much appreciated.