The bigger concern is the potential loss of her B permit.  Is she EU or non-EU?

The biggest concern is the job!Get the job! Once you get into the market. It is alot eaiser to find the job. 

I believe that by leaving CH she is abandoning the remainder of her current B permit - regardless if she is EU national or not. If she then chooses to come back to CH after her stint in the US, she will have to re-apply for a new B permit. This is what I have been expertly advised anyway :-) as I have also been tempted with short stints back in the UK

I'm quite sure having read that you are allowed to go abroad for a short time (< 6 months) without losing your CH residence and your permit.

I believe you can leave for six months officially.. By officially that means informing the authorities.. 

If one plans to keep paying the rent and not deregister at the commune then I guess nobody would know.

yes, even the chomage office will be pleased to allow you up to 6 months to work in a foreign country ( you are off their books as a job seeker ) and retain your "B" or "C" permit. you must however retain your swiss address and health insurance.

but remember, your health insurance may not cover you in the usa, and if you obtain a green card while working in the usa, you are always ( lifetime) liable for usa tax regardless of where you earn your income. ( unless you give up your green card!!)

Indeed, you have to maintain residence in CH plus notify the canton. If you don't - and they find out, the renewal of permit may be jeopardised plus the possible trouble collecting unemployment whilst actually working? Just a thought.