One thing I’ll note about NU is that if, like many engineers, she decides to pivot out, NU will offer more choices. Engineering is the most changed major.
I do think the size, class schedule, location, and money are the differences.
I wouldn’t assume one is better than the other and frankly in MechE ranking doesn’t matter - even to unranked schools. But these are both top level.
She will be somewhere four years so may be best for her to decide assuming affordability.
You also might look at career data. I linked for you. I put wpi to mechE but you may need to reset the tableau if it doesn’t open to it. For NU, you’ll need to ask for more detail. Theirs is not in depth.
Good luck.