If I were in her position, I would take the combined program. I find a great deal of security in the university making the extended commitment.
I do not see why there would be any more difficulty getting a visa for it than for the short program unless - and that could be the deciding issue - there is some financial support issue that cannot be met for the longer program.
Again, the international student officers (not the clerical workers in the office but the main official) at most universities are extremely competent at advising students. If that individual feels that she qualifies for the longer I-20, I would not see any reason not to go for that program.