Oh dcn - I SO know where you're coming from! Exhausting to be "the one" all the time isn't it?- a definite downside to childminding!
Sounds like you're doing the right things and Rea has offered some good advice, too.
I wonder if you'd benefit from a spare pair of hands when this child is with you? When I was pulling my hair out last year, an experienced Nursery Nurse put me in touch with a level 3 student, in her final year, looking for a placement. She was brilliant!
The college tutor visited before she started, the Childminding Network provided the Induction Pack and the lovely student provided an extra pair of hands, a distraction when the child in question was at their most demanding and, perhaps most importantly, a second opinion when I doubted myself! She did separate obs, picked up the same things I had, ran them past her Tutor for extra advice and took part in meetings with the Early Years support team when they came to take an informal look. (She even knew when to step in and put the kettle on!

)
I'd highly recommend it - in fact I've got another student starting after halfterm and another in June

I'd always thought it would be more trouble than it was worth but was glad to be proved wrong!
Nona