Mrs Mercer is not responsible for the UK's standing internationally. The fact Truss has such low standing is a reflection on Truss alone.
I don't view it as childish as I don't see the opposite - biting your tongue? - as adult.
If Truss wants to convince the markets the UK 'has something', she could try being a bit less shit. It is not in anyone's interests to see the UK struggle but I had no say in electing Truss, she has been foisted onto us all by the Tory party. I am not going to bite my tongue and pretend all is dandy while they weaken the UK even further.
Truss has appointed JRM as Business Secretary and he is going to destroy the economy with Truss's full support.