Thank you for that support and advice @mrskode. That is really insightful and helpful. I imagine it must have been a really difficult time for yourself and your family. Your son is very lucky to have such a persistent, caring and patient parent 
Oh @Debsy7680 I hear your trouble! We just want it to be over and they are living day to day. Big hugs.
I still have to give my 19 plenty of notice about big changes in our routine. Guess what? He is now living 1800km away on Uni campus (wouldn't cope with independent living yet) and loving it. I still get 1am phone calls about exam time but everyday is better. When I think back to what he was like as a toddler to where we are now we should be calling ourselves miracle workers. Having said that, at the time, at the worst times, we couldn't see an end and if someone had told us how long it would take we would never have made it this far. My message? Every day is a little better or different. Sometimes the goal posts move. They can move back. And it doesn't last forever.
Another thing to consider is that girls are 'copers'. They manage to get through childhood because they have higher emotional intelligence than many boys. So it might be worthwhile having a full medical check. Hearing, vision, psychological. What are they looking for? Auditory or other processing disorders, executive functioning skills, giftedness, allergies/intolerances, higher functioning autism. Our eldest was informally diagnosed as high functioning autistic and gifted. We didn't share that with others unless it impacted his day. As I have experience with similar behaviours we didn't need to get him coaching etc and he was very high functioning. He actually turned to me the other day and said he could have Aspergers and his sisters basically laughed and said duh! Where have you been? How does this apply to your daughter? Girls are often diagnosed in their teens with autism or similar and anxiety is one of the bigger signs. Now I am not saying your daughter has autism just that there are other reasons for mental health to take a nose dive. It can't hurt to consider and look into it.
Also if the counsellor isn't making much progress maybe she could change to another one. Is there one close? Maybe online. We have had great results with EMDR.
If you can't get away to look after yourself take can you take her with you? Talk about why you need to go for a walk, gym, shopping, book club, coffee. She can sit in the corner and read, or take part, especially the walks. One day you might hear, "Do I have to come?" It is the certainty of where you are and that you definitely coming back that gets reinforced this way. Has she lost connection with someone recently?
Giving her fewer choices while at home can also help. In a reverse psychology sort of way. She can only watch TV shows you like, listen to music/podcasts/radio you prefer, use certain websites, do extra chores around the house, reduced access to social media etc. This can have two outcomes - it can help reduce anxiety as she doesn't have to make these choices or she can start to say this sucks and get out more. Not my first recommendation but it might work for you.
You could verbalise your thinking about things so that she can hear how you work through your own struggles. Man did I get a reaction when I sat down at the table for breakfast and went through all my thinking for the day and that I didn't want to go to work! There, there Mum don't catastrophise, you'll get through it. Now get ready. That came back to haunt them 
But seriously, it helps to know they aren't the only one and it means she might share more with you.
You have found a great forum for support and ideas. Some days I just visit to know that my day isn't as bad as I thought it was. Take care and good luck.
