Extremely shy rescue dog - need advice

I'd rethink taking her to the adoption event this weekend if at all possible. Give her some time and let her adjust to her new situation. She's just had her world rocked. I'd let her shut down, let her settle in, before you start subjecting her to new stressful situations. Let her get to know you and trust you. I wouldn't push her, I'd just let her do her thing right now. I wouldn't go out of your way to accomodate her, but I would let her settle for a couple weeks before you start pushing.

Try a cue word. Like "yes". Instead of c/t it will be "yes"/treat. (but try and use a less common word that she won't get confused with.) Orrrrr use a clicky pen. Or click from in a pocket. Hopefully she'll learn click = treats (make them REALLY yummy, hot dog or something).

Once she has settled in, try using the clicker outside instead of inside and when she isn't right beside you. If you have another dog, clicker train it with her near by, but don't force her to be close, if she comes closer give a reward.