How do I ask my new boss for a break?

I would just tell her that I have a lot of stuff to unload and unpack, and if I were working, I would not be able to put forth my best efforts at work while I am also working at home unpacking my things. Tell her that you don't want to start off on the wrong foot by not being able to work as hard as you can and if she would just give you a week after you arrive to get your things in order, that would be superb.

Honestly that should have been worked out before you accepted. But now that you are in, I think you should go when you are supposed to and explain to her that you will need a few days to adjust. Tell her you are willing to work from home while you set everything up or work half days for the first week.

For future reference though...you need to talk about that stuff beforehand. Since you got the job through a family member I'm sure the boss will understand that you couldn't personally ask for the time you needed...you can even explain to her that you didn't think about that issue until now and ask for the time off in an email or something, but it might not look good. The best bet is to wait til you show up and talk to him/her face to face.

Explain it just as you've explained it here. You are moving and while you are overly grateful for the position and the opportunity, you worry that with the move and acclimating yourself to a new area, that you won't be able to perform fully. Ask the employer if it would create a hardship for them if you were to take a few days or a week to get everything settled so that you could dedicate yourself fully to the position.

It is perfectly normal to ask for a small period of time. You don't even need to give a bunch of excuses, just ask if you can start the following week so that you can get things settled. If she's ever moved at all, she should understand. It isn't unreasonable at all. If she says no and acts like its unreasonable....maybe you don't want her as a boss anyway??

I say report to work to show you want to be there. After that, ask when would be the best time to take a few days off just to situate yourself. Living arrangements do take time and employers normally understand this.