You could try having playtime and/or a leisurely walk on a moderately overcast, somewhat windy night. Of course, I would NOT recommend going alone. Make it as fun as possible. However, you'd have to wait on the weather.
You can purchase CDs specifically for socializiation that will help ease their fear of storms. I know I have a link somewhere but I can't seem to find it. I'll google it and find a supplier. Basically these are just recordings of storm sounds. You can play them (at LOW volumes) at first, at random times. For instance, turn the CD on with the volume barely audible or just louder, and play with her. Leave it on and let it repeat. If she's anxious, you could turn it down a little more. Once she's completely fine with it at that volume(which could take hours, days, weeks...depends on the dog), then turn it up just a little more. Again, once she's used to it at that volume, turn it up more. Keep going until she is comfortable at loud volumes, and then see how she is going out in it(starting with a mild storm). I do suggest dicussing natural sedatives with your vet, or peppermint oil as has been suggested. I know they make ear plugs for horses for the loud environment of horse shows, but I really have no idea if they do this for dogs. You can use cotton though to muffle the sounds of the storms if you have a storm in the middle of her progress. You don't want her to regress.
I'll go find that link. :dogsmile:
Edit Aha! Okay, you can go to dogwise.com and search "storms." The results are a book called "THE BIG BANG! How You Can Help Your Dog Cope with Thunderstorms and Fireworks" by Claudeen McAuliffe, and a "Sounds Good" CD specifically for thunderstorms. The "Sounds Good" line of desensitization products are the cheapest that I've found, but I haven't bought them.
This is actually sold by a horse trainer, but would be good for dogs too. However, this one is not just thunderstorms.
This is made for dogs, a 52-minute CD of thunderstorm sounds.
Audio CDs when used correctly along with natural sedatives can do wonders for dogs with storm anxiety(or horses who just don't like noise). ^^ Good luck to you!!!