I love history and completely get why you would want to study it, but honestly the history grads in every industry may not be doing anything related to that major. Do most go on to get more advanced degrees? You need to think about that and do more digging. Why don’t you try talking to Brown history dept/Brown history majors. My guess is if you came up with an idea of possible career goals and minor/internships that could help hone your path your mom’s concerns about Brown would be greatly diminished.
Also, I think you need to really evaluate your mental health concerns. Are you just uneasy about leaving your comfort zone or is there more to it? I think many kids are feeling like they want to be closer to home these days.