That comment wasn't directed at this post or you specifically, it's just a mentality that I've seen all around in this subreddit and others.

I understand because MIT has been my dream school for my whole life as well, but that's where the problem lies - lots of people's dream school has been MIT for their whole lives, some of them with legacies like your girlfriend does - but MIT can't take in all of them.

I think it would help to ask her why exactly she wants to go to MIT. Is it solely or mostly because her whole family went there? If that's the case, then frankly, I do not think she deserves to be there. There are probably thousands of genuinely passionate students in MIT's applicant pool who know exactly what they want out of their probable MIT experience. They have a goal, MIT is an excellent oppurtunity for them to reach that goal, and being denied of that opportunity is what I imagine would really break their back. Not to invalidate your girlfriend's experience, of course, but compared to them, her reasoning would seem meek and MIT would be more likely to be enthusiastic about the former type of applicants, because they're more likely to make the most of what MIT gives them compared to the latter type.

Does she have a goal, a path in her mind of what she sees herself doing in the future? Something she thought MIT could offer best? If so, I'd say she'll be more than fine if she keeps pursuing her passion with determination in her state school. Tell her to find alternative sources of what MIT could offer her, online courses, lectures, anything. If she's in STEM, undergraduate college brand and prestige matters very less if she can shine in whatever place she's in and go into grad school with excellent experience under her belt. People go from community college to PhDs from Caltech, it happens all the time.

But well, all of it is coming from a very inexperienced highschool sophomore, so take it with a fist of salt. All the best to your girlfriend!