I would agree with many of the people above who suggested some sort of sedative, whether it be herbal or prescribed. Just enough to take the edge off so you aren't worried about what is going on inside her. I don't think you are ever really going to be able to change her behavior, but you both may feel better if she seems a little calmer during the storms. My parents had a beagle that was petrified of storms and would hide in their bedroom closet. The first few years I think they felt just horrible about the poor dogs fears. After a while, they accepted the fact that this was how she dealt with storms.