Welcome to the forum Mel! My name is also Mel and I have a 6 month old pup named Ginny
I've never had a rescue dog but have delt with some shyness and loud noises.
I found it really helpful to desensitize Milo and Sadie to the things they were afraid of. Milo was terrified of other dogs and of loud noises so I enrolled him in a puppy class at our local Petsmart. Petsmart is full of all kinds of loud noises and I figured puppies were less intimidating that adult dogs (Milo was also 9 months old at the time so technically a pup). Sadie was overwhelmed by simply the loud noises.
Petsmart felt very overwhelming to both dogs for a while so I started by bringing them in for short periods, giving lots of praise and high value rewards, then leaving. Gradually I increased the duration, for both dogs, till they were no longer afraid.
If Ginni isn't already crate trained, I'd definitely consider it. She may find it comforting to have a place all her own to hide. When you're not home you can put her in her crate.
Others on the forum have found it useful to record the frightening noises and play them back at a low level when they're not home. You may want to combine that with crate training, when you're not around. You can gradually increase the sounds as she gets comfortable with them.
One more word of advice that you may already know through your training, find what motivates your dog. If your dog is food motivated find the treat she'll do anything for and use it as a high value treat You can also use toys or games that she loves as motivation. Tug can be particularly useful, as it can not only be a reward, but a way of bonding with her.
Good luck!