A good rule of thumb about bringing things up is: If there's a question about whether to say it, don't. The reason for this is that there are no questions in God, and there are no questions within the peace of our heart. If you are "weighing" whether to say something, you are consulting your conflicted mind instead of your peaceful mind, and this is never necessary.
Jane's mother has already asked her to attend college with her. For you to tell Jane that her mother does not have her best interests at heart is to assume that you possess wisdom that none of us actually has. If Jane herself brings this subject up, you can of course give your opinion. But do not try to convince her that you are right and her mother is wrong.
It is interesting that even with something as straightforward as applying to college, none of us is in a position to know what is best for another person.
If both of us had not dropped out of college for a year or two (which our parents advised us against), we would not have met each other; we would not have had our two sons, and so forth. That doesn't mean that other good things might not have happened if we had followed our parents' advice, but the point is, none of us are in a position to know what would have happened. Who can know how the tiniest decision will affect other people, how many it will affect, and in what ways? We all have enough trouble just figuring out how to run our own lives, and eventually we learn to turn everything over to God.
The one sure gift that you can give your granddaughter is to trust her and to trust God's presence in her life. As her grandmother, you can safely practice unconditional love and faith. Even if there is no one else in her life to fulfill this function, be the one who she knows will always love her, no matter what she does or fails to do. This, in our opinion, will do far more to help her have a whole and happy life than taking a stand on where she should go to college.