Bless her, our stray is terrified of loud noises, hates fireworks and just hides, he still has his little hang ups after 7 years, still won’t get in the front of the car (we think he was dumped out of a van) but the separation anxiety worked itself out once he got to know we loved him and would always come back.
I’m not well up on training techniques, but we just left for short periods and came back, and kept repeating every few days so as not to overwhelm him, never making a big deal of leaving or coming in, just quietly going out and quietly coming back in, ignoring any stressed whining or excited behaviour on our return and we completely ignored any mess he made, and just cleaned it up, and after a while he was happy to be left, hopefully the training will have some success but it could be too soon to properly work effectively, she’s still getting used to living with you so it will probably take time and a lot of reassurance & consistency.
A good excercise routine helps too, with ours the more worn out they are the more they are happy just to get on the sofa for a nap and not care what anyone else is doing!
do you know her history? It could that if she got a too excited during play or in general she could have been told off, excluded or even punished, so it may be a bit of a trigger for her? like everything else though, she’ll learn about you as you learn about her and as long as everyone is calm and consistent she’ll learn to trust and love you all.