Hello James,
It is NEVER a good idea to lie to an immigration officer. End of.
So, she should just tell the truth.
I was never asked if I was employed in the USA, but I was. I was also in school. I did not bring evidence of either of those things, but looking back, I should have. Because they can ask for it. I just didn't know!
Even tho she is quitting her job, she probably has plenty of evidence that she has ties to her homeland... Like, an apartment she is renting, or a car lease, or perhaps a pet? I don't know what she needs, and what applies, but she should bring evidence of ties to the US in case she is asked. Someone on here will know more about what counts as 'ties to the US.'
Also, she should not bring a CV, or her diploma, or anything like that - nothing that would make them think she may be job hunting while she is here! If you want to be really paranoid, be mindful of what may be on a laptop, if one is being taken into the country.
I came through immigration so many times, and they did not stop me or question me at all. I wrote the amount of money I had access to for the duration of my trip on my landing card, and I always had enough to support myself while I was there. It was never questioned. I always had my return ticket, and I said what my mom always said when we travelled together when I was a child - Simply because she always said it, so I just automatically just said it too. I said I was 'visiting a loved one' and if I was asked if it was a romantic relationship I would have said YES, but for whatever reason, I don't think I was never asked. I may have been. But, some people have suggested that saying that to immigration might sound 'cheeky' to them, and they would therefore not suggest using that phrase. They think it is just better to say 'Boyfriend.' And although it was never an issue for me, they may be right!
There is no reason to hide the fact that you are in a romantic relationship!
It is not illegal at all.
xoxooox,
L.