This is a tough one. Separation anxiety/general anxiety, in our case, was the worst symptom for our daughter. I remember like it was yesterday not being able to go to the bathroom without her following. Her gran couldn't even get to take her out without mum or dad going. Luckily, it did eventually improve with 6 months of prophylaxis abx but was the last symptom to improve. Even now DD doesn't have the confidence of her peers. They are all having sleepovers etc., but DD isn't anywhere near this.
Take small steps and try not to show how frustrated you are (hard as this is). It really does improve with time. You won't be at this crisis point for long. Improvement for us happened very gradually. One day at a birthday party I thought how great it was DD went off to dance on her own without holding my hand! Then she sat at the dinner table with her friends and didn't notice I wasn't stood behind her. Went to the toilet on her own without a second thought.....
DD overall is 95% better since major episode 2 years ago She still takes prophylaxis for now and she will have minor relapses with viruses etc. But, despite separation anxiety being the one symptom we see decline first when she gets ill, it is nowhere near as debilitating. She just gets more nervous and on high alert for a week or two. No - she's not like her friends quite yet. But she did stay at a friend's for tea for a whole 2 hours last week without me - and didn't want to go home when I turned up to collect her! She was so proud of herself and because it went well for her (i.e. nothing 'bad' happened and mum did come back), she is now primed to do it again soon. She is actually looking forward to the next time. She will just be much older when she does all the independent things like sleepovers at friends.
Word of warning though, I have been seeing a therapist to help me cope with PANDAS PTSD and I have discovered how much of an influence I can actually be on my daughter's anxiety. Without realising, I have been just as nervous as her (or worse?) at the thought of her being independent ('oh my god, she couldn't possibly do that.... worry, worry, worry.....people don't understand, that will set her right back'....etc. etc. etc.......) All those thoughts I have because I too am scarred from years of rollercoaster behaviour and trying to prevent disasters. We, as mums, have a duty to protect. This is our second nature and we do so many things we are not aware of. You are now programmed to condition the environment to your DD's needs. It doesn't matter she is getting so much better, fresh in your mind are those awful reminders of worse times. When will it happen again? Be mindful of the fact that we influence our children so much: I didn't know I was holding DD back until a stranger told me.
I hope things improve for your family real soon. Hang on in there............