My parents are both teachers and as children in their house, we had to attend school till the very last second. I am for sending them there. It teaches them that even though you have nothing at work to do for the day, does not mean that you can stay home and sleep/watch movie, kwim. There are some days that you have little to nothing to do at work, but you still have to go. Does taking your child out of school early, because there are no more work for them, not teach them to be lax and not take responsibility? In a work situation, you would not like it when at the end of the year your workers does not pitch because "it's the last two weeks of the year", kwim??
I know it sucks to go to school the last two weeks of the school year, but is it really THAT bad. Not one of my sisters or I had ever been truant - in high school (what they did at uni is a WHOLE other story). If you were sick, you went to the doctor and got a letter. If you were not that sick, you go to school and if you feel worse later in the day, you ask to be excused. It did not make me a bad person. I don't feel that I wasted that week or so. I feel proud that I attended school as were expected of me.
I have to say that we did have LOADS of fun in those last week. We would have informal watersport competitions, have class BBQ's (sorta like a chrismas party), we cleaned the school and the boys repaired desks, we would practice sing-songs for the next year, have talent shows, some teachers would even begin with the following year's work (no kidding) - math and accounting. Our reportcards were handed out on the very last day, the very last period. If you were not there, you only get your reportcard the following year!!!!!!
If you really want to take her out, let the school know that she is going to her nan's and that her "lift" leaves on that and that date and it would not be possible for her to attend. That is just good parent-teacher relations. IN MY OPINION!!