Just think of it this way: (not that I want to sound harsh toward you) but, if she gets into the garbage, that is not her fault. She hasn't been taught. If dogs are taught things and taught in a way which makes it worth their while, they tend not to engage in those behaviors. For instance, getting into the garbage has the promise of a payoff, right? She's probably been successful before. Dogs do what works. It's how they survive in the wild....doing what works. So, you have to make in impossible for her to succeed at getting that payoff....getting into the garbage. She must never ever have a success. Then she'll not get into that habit.
Take her off the table, gently, calmly, saying "off" and when she is down on the floor on all fours, praise her. Prevent her from getting on the table. If she looks like she's about to get on, or thinking about it, re-direct her to another place and praise for that. Be super consistant. If she gets the payoff for getting on the table (it must be fun for her) then that reinforces that behavior. Always prevent a payoff for any unwanted behavior and give a payoff for wanted behavior. Again, be patient and don't scold. She can learn this way.
When she is doing something that you don't like, instead of scolding, go to her and re-direct her...get her attention and show her an alternative behavior which she can do instead. Scaring her with noisemakers, startling her, being loud, making quick movements are all things which this dog, really, no dog should be subjected to. It doesn't teach. It only creates fear and distrust of her owner. So, in other words, show her what you want her to do instead of the undesireable behavior. Give her an alternative. And praise her for that. This will cause the undesireable behavior to extinguish all by itself. You don't have to scold.
With potty mistakes, again....that is not her fault. She doesn't know yet well enough. She must be confused. Take her out more often. Watch her when she's lose in the house so she doesn't have an opportunity to go pee inside. Praise her right the second she's done peeing outside. Even if you catch her in the act, don't say, "no." She's one timid dog. Just pick her up right away and scoot her outside, then praise if she goes outside. Give a command while she's going so she learns to go on command (if she has to go at all). If she's nervous, keep your praise low key. If she likes a squeeky voice, playfulness, then do it that way. (remember that when you tell a dog "no" or scold when it pees or poos in the house, the dog may interpret this to mean that peeing and pooping is bad period...not that it's bad to go inside) This can make a dog hold it and hold it and not even want to go outside. Finally it can't hold it and it hides behind furniture to go. It causes fear in the dog. So, don't make a big deal out of it if you make a mistake and not take her out often enough. Just clean it up and forget it.
To be a good leader, be calm and confident, fair, gentle, no scolding, motivate and reward her for behavior you like, distract and give alternatives for behavior you don't like. Teach her some little basic obedience skills (that builds confidence and makes her look up to you). Make training fun and rewarding. Dogs usually love walks. Take her where she is comfortable and not afraid.
I don't mean to sound bossy, but that's my writing style. LOL. I'm just writing things as I think of them and trying to give you some tips. I hope it helps a little. You have a timid dog who is a special needs dog and it takes oodles of patience. Kudos to you for taking her on and giving her such a nice home and caring for her. I hope things will improve for you.