As others have said, Wellesley College and Northeastern University are quite different, but they are both very good schools. Both can be quite expensive unless the student qualifies for significant financial aid one way or another. Both are very well respected and have very good reputations.
When I hear “premed”, two things come to mind. The big one is that medical school is very expensive, and for admissions to medical school you really are not likely to gain much, if anything, attending an expensive and famous and highly ranked school versus a more affordable and maybe slightly lower ranked school for their bachelor’s degree. The other thing that comes to mind is that the majority of students who start university thinking “premed” end up doing something else. Some cannot maintain a medical-school-worthy GPA in the tough premed classes. However, many students just decide that they want to do something else. A few for example might get into lab classes, find they love it, and just decide to do lab-based basic research.
One plus with this decision is that Wellesley College and Northeastern are both very good for a wide range of majors in case a student decides to do something other than try to go on to medical school.
At least in my experience, having years ago been on the other end of the MIT-Wellesley exchange bus (and having ridden the bus for a couple of classes), is that Wellesley students do get into Cambridge from time to time.
And I think that it is a really good idea to visit both schools. Finding a school that is a good fit is very important, and fit can be hard to judge until you are there and see it.
Finally, make sure that you are not going to be spending so much of your college funds on undergrad that you will be unable to help with the cost of medical school. Attending a different lower cost school might be a very good idea if medical school is going to work out, and if you need to do this to be able to afford to help a LOT with the cost of medical school.
We for example would not let our daughter attend NEU because it would have been too expensive for us, but then a few years later because of this were able to help her quite a bit with the cost of a DVM. At one point we had a frustrated high school senior. A few years later we had a happy and thankful DVM student (who is now a happy and thankful veterinarian).
One doctor I know said that other students in his MD program came from “all over the place”. Another said essentially the same thing. A daughter who is currently getting a biomedical PhD has found that the other students in her program came from a huge range of colleges and universities, including Harvard, NEU, a top New England LAC, U.Mass Amherst, U.Mass Lowell, schools all over the USA, schools outside the USA, and a very wide range of other schools many of which are lower ranked than anything that I just mentioned, and a few of whom I had never heard of. In terms of ranking the difference between Wellesley College and NEU will not matter for graduate school or medical school admissions, and frankly the difference between either of these schools and U.Mass (whether Amherst or Lowell or probably even Boston) will not matter either. What a student does as an undergraduate student will matter a lot. Where they do it really does not.
I would not worry at all about any perceived different in ranking or “prestige” between these two very good schools.