What do I tell the lady i babysit for?

OK, i babysit reg. for a lady who has 3 kids ages 6, 4, and 2. it used to be, she just called me when she needed me (it was about 2-3 times a week), but now we have a schedule so that i watch them every Mon, Tue, and Fri night. the past few times i was supposed to watch them, the kids have been sick. i heard they were getting better yesterday, but i don't know whether or not she feels comfortable leaving them tonight and if i still need to go over. I woke up with e snooky nose and cough (i'm 16) and my mom said she doesn't think it would be a good idea for me to watch them until it clears up. I sent her an e-mail just now, and i am about to call her to tell her that i can't babysit tonight if she needs me, but i am very shy and i tend to freeze up. can someone write out what i should say. (in your answer don't say "just tell her what you told us"), write out like a dialogue for me. so she says "Hello", and I say "Hey Mrs. Stacey, um...." you finish. thanks.