The one main thing I can tell you is don't "comfort" her too much when she's scared. That's actually just going to make it worse because you're giving her something positive when she's scared and it's reenforcing it. I know it's super hard not to but the best thing you can do is just stay calm and do whatever you have to to not feel sorry for her at that moment. Then try distracting her - if she knows some basic commands, see if you can get her to do some; something to try to snap her out of it and behave normaly. If you cuddle and pet her and get nervous about it she's kind of thinking, "Oh no, she's scared too". Our Akita gets nervous with loud storms and when I see her looking around or getting up to want to start pacing, I just tell her "no, it's fine" in a very steady voice and make her lay down where she was and then she's fine. If you stay calm and uneffected by it they will follow suit, especially if she's really attached to you, that makes it easier because she'll "feed" off your emotions. And of course, if she's really bad and nothing you do will distract her enough you have the option of talking to your vet about a mild sedative to use when there's a storm, but I'd make that a last resort.
The barking at your bf, I'd just gently but firmly correct it the moment it happens. Even if it is out of fear (most dog's behavioral issues are fear based), just correct it so that's letting her know 1 there's nothing to be scared of 2 this isn't allowed. Also try having him feed her sometimes and take her outside to potty or for a walk. My pup is my first Yorkie and she's been fear barking at all kinds of things (even a horse on the TV the other night lol). I just correct it every time with a firm "ah ah" or I'll gently but quickly touch the side of her neck with 2 fingers. Then when she stops and calms down I pet her to reenforce the "calmness". She's sooo much better now after only a few weeks. Definatly don't pet or cuddle her in those moments or she could end up becoming agrressive towards him.
I'm by no means a professional trainer, but I've done tons of research on behavior things like this since our Akita was a submissive urinator and had seperation anxiety. We socialized her really well and exposed her to all kinds of different places, people, noises etc. (which I'm also doing with my yorkie now)as well as doing the things I mentioned above. Now she's really good, loves everyone she meets, is extremely affectionate (she hid in her kennel the first week we had her) and is very obedient and happy
I know an Akita seems like a far cry from a Yorkie, but as I've learned by working with my submissive Yorkie the past month, dogs are dogs when it comes to this stuff.
Hope this helps, good luck