Beyond what the wage is right now, she might consider her marketability for other positions. You will find yourself in demand as an RN all the time, and have your choice of where you'd like to work. She will be limited in her selections, that's just how it is. The need for LPNs in nursing homes isn't likely to diminish at all; if she wants NH work forever, she'll be just fine with the LPN. But if she's looking only at the dollar income today, she's short-sighting herself (and potentially her son).
I don't want to start a debate with others about all the places LPNs have found work; I'm speaking generally.
Ultimately the choice is hers, and you shouldn't sweat over it. Do your own schoolwork, she'll do hers and you'll both get jos and compare notes. If you're very lucky, you'll both be happy whatever choice is made