12 year old daughter - family impact

Hi. I’m not sure if anyone can help me. I have a 12 year old daughter who I think is showing signs of autism but masks at school and isn’t getting any support. At home it’s a living nightmare. She is aggressive, angry, paranoid and we just go from one issue to another.  Not liking to eat with us anymore because we eat loud (we don’t), hardly communicating, being so paranoid about how her dad or bother look at her, storming off for no reason not wanting to be in the same room as anyone. Things are so much worse since she Started secondary school last year. She frequently leaves class, is so anxious about any tests or being called out for anything even if it’s good. Life is very difficult. 
we can’t do normal family things anymore. We’ve tried to get some help but it’s been impossible so we are paying for a counsellor to help with her rage but it’s not making a difference. 

is it worth a private test for autism? We will try and find the money but will it give us support if positive - and if not where can we get some? We are desperate.