So in effect they are coaching people to lie under oath? You are right, it is best to be truthful, but that does not mean she has to include information not asked for.
As to a B2 application, the consulate officer is to assume an applicant will overstay by law. It is up to the applicant to overcome this assumption. Now an applicant is not required to supply evidence not asked for, and to my knowledge the DS160 only asks about family members in the U.S. (I could be wrong), but consulates do their homework, and they will know if an applicant is communicating with someone in the U.S. back in 2013 my now wife applied for a B2, and even though she did not mention me, the consulate knew about me probably from our communications.
I agree, applying for a B2 is not expensive, so go forward. Just make sure she does not materially lie under oath at the interview. If the CO asks about you, she needs to acknowledge you.
Good Luck!