germs - advice and support

Hi all 

I have a 11 year old autistic daughter. She has been amazing in everything , happy and managed well in school and life in generally. Within the last month she has started to become very obsessed with at first food allergies  she has peanut and sesame allergy so this is understandable. But now this seems to have switched to germs and not being clean. She is refusing to touch things, open doors. Instead she is always wanting to wash her hands, crying that she is not clean.

She is transitioning from primary to high school and I understand that there is lots of change in her life. She seems to have coped well at the high school days. But the leavers assembly of primary has just made this germ / cleaning fear off the scale. It feels like its gone for 10 -100 overnight. Hysterically crying, fear of germs going to kill her and us .

She had a school residential and I feel that was the catalyst for this reaction.

Its heart breaking, she has gone from a happy caring girl to sad and isolating herself who cannot be consoled 

Really I am look for anyone who has any experience with this , and how they managed. She isn't open to talk about it or rational advice. I really don't want to stress her more with the wrong approaches, It feels I am getting it wrong. 

Thank you in advance , any suggestions welcome