You print of a letter and have it ready for pick up but you discuss the situation in person first and then you hand her the letter and say this letter is for your records .
Have a point form list of the things you want to say so that you don't forget to mention and you don't stray off topic .... I'm hoping you have already discussed a few of the issues with her that you've been having since he started..... This will likely not be a surprise as you are probably not his first daycare to have been termed from