You are obviously upset and cross about what has happened. And I'm not trying to say that you aren't.
But you have also said that you're not going to tell your nanny any of this.
She deserves to hear your views
a) because if she's no good at her job then she deserves to know why, so that she can work on her skills
b) so that she understands that she is not doing her job well
By not telling her you are doing two things. Firstly you are not helping her develop her skills as a nanny.
Secondly you will undermine her self esteem.
Why would you not talk to her about this and how you feel? You are obviously angry about it - you are taking it out on me!
I'm not making stupid accusations - just pointing out that she deserves better.
And if she's that bad, then it is important that you tell her, otherwise other employers will also suffer.
Why wouldn't you tell her these things?