Luke was able to defeat her only because he is champion of the light side and expert in defending against dark side powers. Only he was able to reach her with lightsaber. She was tearing apart sith. Grand lord of the lost tribe ended up beheaded as well.
Abeloth does not have control over light side. Darkside is her field and it would be Palpatine entering her field since she has much more raw power. Force lightning doesn't work on her. If he tried using force storm, he would only give her favor by showing such a wonderful technique. The only thing that would keep Palpatine alive is his lightsaber.