Don't tell her you can't ... tell her you're not interested at this time.
How do you know you can't do it?
Then it's respectable to say that you're not interested at this time. Thank them for the offer. You don't need to give a reason.
Be professional. No negative feedback. Give them gratitude for the offer and politely decline. You are not ready to leave your current position or whatever. Leave the personal conflicts out of it. Good luck to you!
Why do you think you cannot do the new position? Maybe your boss sees potential in you that you don't see.
Yelling, in such a situation, is abuse and not tolerated! I would tell her that if she EVER yelled at me. Be strong, set your professional boundaries, and persevere. Best wishes.
Wait, wait, wait a minute........how do you know you can't do customer service admin? Tell me please.
Ohhh, I see now. I wish I had a good answer for you. I think I would tell her what you just told me.
That's a really difficult question - I used to be the boss offering the positions.
On the one hand, this is a good step up for you and she thinks so highly of you that she believes you can do it, so if you refuse she's probably not going to feel quite the same about you. She may see you as lacking ambition.
And what about you? She obviously likes your work, so what makes you think you can't do it? You may be very surprised, it may be the perfect job for you. If it were me, I'd take a chance on it. I did that once, was offered a position I was wildly unqualified for, Personal Assistant to the General Manager. He believed in me, and man, was I good at that job. Great money, lots of perks, headaches, yeah, but how I loved solving them. I really grew with that job.
You say you hate that boss - but have you given a thought to what this can do for your future? I found a way to get along with just about anybody, and I've never regretted it. After all, you won't be there forever. Maybe you'll get THAT boss's job someday if they're a real shite. I don't recommend that you tell anyone at work - particularly your boss, that you hate that supervisor either way.
I think you should do it if at all possible. If the hours are the issue, tell her and maybe something could be worked out.
tell her you dont feel comfortable with doing it b/c.........