I don't imagine that you have control of the fact that Daddy is gone for 6 weeks, and unless you're interested in homeschooling, you need to send her to school. They've addressed the boredom in school with the change to first grade subject acceleration.
The thing that you do have control over is that she's tired, and you know that she acts better after a nap. Overtired children are fussy/tantrummy/miserable . . .
If she can nap every day, or even just an extra day or two out of the week, that might improve the situation. The other thing you can do is to put her to bed earlier -- even 20-30 minutes earlier might do the trick. Overtired children don't sleep as well, which keeps them overtired.
Great book:
Healthy Sleep Habits, Happy Child by Marc Weissbluth
Written by a physician who specializes in pediatric sleep; very science-based; no kooky gimmicks.
parenthetically: (we use melatonin from time to time in our house, it's well studied in kids and comes as a 2.5 mg chewable)
Good luck!
