Oh bless her, I'm so glad she has found you and can now have a normal and happy life. Certainly, it will take time to adapt to her new homelife and we will need to be patient and gentle (as I'm sure you are!).
I suspect it is alien for her to have a lead on, be around busy streets and to walk for exercise and enjoyment; each of these things is a separate hurdle to overcome.
It sounds as though she may also have developed a noise phobia, which we will need to work on with her.
You have absolutely done the right thing to not force the walk as this would make things worse and escalate her stress levels. We need to dial it right back.
It is tricky Re the toileting, but I would continue to use that patch for now and reward heavily when she puts on the lead, leaves the home, walks to the patch, toilets and gets home. Each of these milestones deserves a 'Great girl!' and high value treat like chicken.
You can work on de-sensitizing her to the things that cause anxiety but do take it very slowly. So, for example, you could attach her lead and walk to the front door, then reward her if she remans happy and confident. If she becomes stressed, we need to take a step back. Over time, we build on what she can do so, after a week or two of building on getting to her toileting patch, we may see if she will walk 1-2 feet away from it (lots of rewards, 'great girl!') and then back in. It's all about positive experiences, building trust and her understanding that something lovely happens when she takes that one step further out of her comfort zone.
A similar technique can be used with noise. You can play a You Tube video of a noise road for example, and reward her when the volume is very low and she remains calm and settled. Gradually, over days and weeks, play the sound at slightly louder volumes, rewarding heavily as she tolerates it. If she becomes unsettled, we have taken a step too far and need to dial it back.
Be sure to bring her to the grassy patch when noise levels are at their lowest and, ideally, have a set routine so she knows that e.g. she is always brought when she wakes up, after lunch, before bed etc. as anxious dogs LOVE routine.
We can work on building her confidence in general with things such as natural calming supplements e.g Zylkene, a plug in like Adaptil, basic training commands (sit, stay etc), easy food puzzles she can solve, lots of play and lots of fuss and bonding time (if she enjoys it).
Holding in poo can lead to chronic constipation and, less commonly, bowel enlargement, Holding in pee can cause urine infections and stones. It's difficult to say if it is worse for her to hold it in, but I would try and allow her access to that patch as much as is necessary and work on hard on making it a positive experience every time.