Business Visa For U.s.

My sister is going to attend a meeting in US, she has an invitation letter from her company in US saying the meeting period is between Mar 6-10. She wants to stay a few more days (4-5 days) there after the meeting for travelling. In US embassy website mentions that "Your purpose of travel must be purely business or pleasure or you are not eligible to travel with a Visitor Visa"

What does that suppose to mean? Does it mean if we apply for a Business visa type then we can stay longer for travelling??

A few questions here:

1. In DS156 form requires us to fill up how long we intend to stay in U.S. and for what purpose - how should it be written? 1 week business 1 week tourist? Or 2 weeks business?

2. If we say 2 weeks, will they question why you are going to stay 2 weeks while the meeting is just for one week only??

Well, I am sure there must be many people doing this before so .. pleasssse help to advise me so I can tell my sister!!

bambi