I've seen similar situations and my suggestion is give two weeks notice. No more or you are sure to be replaced sooner rather than later. Two weeks is the correct notice. Be proactive in finding a replacement. Offer to do interviews etc. Teach your replacement as much as you can for a smooth transition. Hey, life changes! Anyone who expects someone to continue on the same job till they retire is not living in the real world.
If there is drama and stress, just remind yourself its HER drama...HER stress. You are moving on. Good luck!