[justamom]

Reread your post so this is the edited part HOW MANY REQUESTS FOR TIME OFF HAVE YOU MADE? Barbara has a good approach.

This is the original
First, pretend you are going and WILL lose your job. If this is an acceptable outcome, the rest is easy. WHY? Because you've accepted the WORST outcome and decided you can live with it.

If this is true, then it all boils down to how you approach the lady.
You can be calm and in control of the conversation because going is more important than the job. You won't have to plea or get emotional. If you really CAN'T bear to lose the job then you don't have any leverage. You must be sure.

Lets say you are going to go-
Mrs. Gottawork, I have been thinking about my request and the reasons you denied it. I would like you to reconsider based on some information you may be unaware of...fill her in on the actual event with your family, don't mention Turkey Day... how you've never asked for time off in so long...maybe somebody was hired AFTER you...never missed a day. If it is within your means, offer to pay for a substitute teacher...(what is it now 32/day)
You have to end on a note of strength. In a sense Mrs. Gottawork, I don't see how you can deny my request. You are asking me to choose between a life event with my family and a job that employs me 2 days a week. Give her a little time to mull that over. If she STILL says no, just say I'm sorry, consider this my resignation.