If your tired and dont want to work anymore, you should stop. I just made a similar decision. And ultimately you have a good reason to not work. Your boss sounds very understanding. You might want to take advantage. If you feel really bad make a compromise and just do a few more days, just remember they knew this was coming and they've had time to prepare. Its out of your control if they are ready or not. I'm sure she is prepared to work more since your leave is only a week away. A few extra days won't hurt her.
If she told you you could be done I would take advantage of that. This will be an important time to relax and prepare. Even though she is nice, it still isn't your responsibility to make sure there is staff. Take it easy :) good luck!