Citizenship is a different issue. The reentry permit would preserve her green card while she is gone for up to 2 years, but it does not build any eligibility or obligation towards citizenship. It is only an option in case she (presumably along with you) wants to move back to the US within the next 2 years.
But if she is already sure she won't want to move back to the US, she can go ahead and file I-407 and surrender the green card at the consulate and forget about the reentry permit. And also apply for a tourist visa in the same visit. After having officially and voluntarily surrendered the GC, she's not likely to have a problem with the immigrant intent issue when applying for the visa, and they'll almost surely give her a multi-year tourist visa.