Isn't happiness what it's all about? I'd be happy living in a tent in the mountains if I could.

I don't have that choice.
Ok what's the worse that can happen if you take the job? Maybe eat some crow, and listen to your sister etc? But aren't you already doing that in her eyes? And doesn't she already rag you?
I say go for it... think things through, get things in writing...you know all that stuff...