People use DAP diffusers, but I've never tried it (I think Lizzie used them when Nikki arrived with them??)
The problem is that we don't get thunder storms often enough for them to get used to the idea that they are safe so everyone is a new, scary experience.
Jon just cuddles ours.... for as long as it takes. But we're lucky that Jon's been here both times there's been a storm lately. I don't think this is something unique to Daisy; my cats are terrified and just hide, just like Daisy. I just let them deal with it on their own, just check on them every so often. And as for the kids at school!!! Screams when there is thunder and I have had one kid who sat under their table and refused to move until it had stopped.
Sorry I don't know more. Michelle'd be a good person to ask as I know her fosters hate loud noises