my bosses wife just got me so mad

I received a notice from my sons teacher, to have his bday party when they return from winter vacation. I received it on Friday and was hoping bosses wife would show up to the office like she always does by popping in. and I wouldhave discussed it with her then. SO I gave her a call cause there was no time on my sons note and she tells me the days the teacher gave me were no good for her. She covers for me when I am not here. She told me what about monday the 3rd or friday the 7th. My sons bday is the 29th. How can I have it the 7th so far from his bday. I do not think it is fair to him. In all honestly I didnt want to have a party in school for him this year. I know thi sis mean but what gaul she has to say it is no good for her. Change the day. This is a kid we are talking about. I hope he will be okay with it thi sway. I am not having a bday party for him. I have one everyyear and each year his friends stand him up and it breaks my heart. So this year I figured we will have a dinner for him and if you want to come pay your own way. Grandparents also have to pay their own way. Im not being mean. Im being cheap. But how can my bosses wife say that? Got me so mad and now I have to write a letter to my sons teacher and tell her the days she gave me are not good for me. How tacky is that? I am so mad angry and pissed