E.B.
With my ds, I had to create a school-like situation. He sometimes wanted to lie in bed in his pjs and just read ("no math today, Mom, ok?" that sort of thing). So I set the alarm, had him get dressed, packed a lunch, and had him "report" to the school room.
Also, you might do something that finalizes, in a concrete way, the end of vacation and the start of the school semester. Sometimes in a homeschooling situation, there just isn't that physical, tangible separation between "home" and "school" in a kid's mind.
Maybe you could go out for pizza or ice cream, talk about the holidays, and talk about how the vacation is over, and how school is now back in session. Ask your daughter what she would like the school day to be, where she likes doing her work pages, etc. Ask her to pretend to be the teacher for a minute. What would she do differently? If you listen carefully you might get some clues as to why she is balking.
Make sure your school area looks like school. If you teach her at the dining room table but it's still piled high with Christmas cards to respond to, or decorations that haven't been put away, that won't be conducive to schooling. And maybe you could go shopping for a new notebook, or some super shiny fun pencils, or something that she could put on her school desk (a tiny cactus plant, or a special little picture frame, or a little kitten figurine or something).