Travelling on a visa to US
I think there is really no general answer to this question. As mentioned before, the visa doesn't mean the border patrol officer will grant entry. He has the right to ask the young lady questions just about anything. He may deny entry and there is no right to apeal for people on a tourist visa.
As a general information: The US Immigration has now records not just about when somebody enter the US but also when he left. So the next time somebody comes back to the US (especially only a few days or weeks after leaving the US) the Officer might asked more questions and grant only short stay or even deny entry.
So, if a young lady comes and leaves the US in a short period of time red flags will come up.
After 9-11 border officer are more careful with granting entry, because each officer gives out an electronic signature when granting entry. If down the road it turns out that a tourist got in trouble in the USA, the officer who granted entry could get in trouble himself and might even lose his job.
I think that is one of the main reason why border officer are now much more careful when checking people before granting entry into the US.
A british friend of mine was recently denied entry, because he keept going in and out. He is in his 60's and on a very goodpension (so no risk he wants to work in the US), I wonder how the reaction would be with a young lady from a considered very poor country.....