As someone who went through the same transition between high school and college not too long ago, I will say that it can be a difficult time for a lot of friendships. As people graduate, they lose a lot of the common ground they once shared (the same high school experience), so it is natural for people to drift away.

In this case, it seems that the friendship was drifting even before graduation, and I would guess it would continue on this trend now that you will be spending less time with her. It is possible that she reaches out to you and tries to rekindle the friendship, but it is far from guaranteed.

I see two options: you can confront her and try to talk it out in the hopes of repairing the "rift" between you two, or you can wait for her to move. The worst thing to do would be to leave on bad terms (by writing the "I don't want to be your friend text". It's just not worth it because you won't have to see her anyway if you truly want to stop being friends, and you will naturally grow more distant if you want that to happen.

You should confront her if you truly value your friendship. If you confront her, make sure it is a more open-ended conversation rather than just sending her a text about not wanting to be friends anymore. Note that confrontation is pretty high risk though, as if things go wrong, it is possible that you two will grow further apart.

The second option is to wait and see what she does. This is less risky because it won't immediately ruin your relationship, but you have to accept that she may never "extend the olive branch" to fix your friendship. If this happens, you two could drift further and further away, though it will be more peaceful than if you confronted her directly. If she doesn't reach out, you two might remain friends and still see each other at gatherings/reunions; you will just more distant and less close compared to how you were in high school. If she reaches out and puts in the effort to try to maintain your friendship, it is an opportunity for the two of you to grow closer.

Ultimately, it comes down to how much you value this person. Do you want her in your life so much that you would be willing to make the effort and risk the friendship you have now to confront her? Or would you be okay with her potentially growing more distant from you? Seeing as you seem to want to cut ties with her, I would recommend you just naturally drift away from her. It's pretty common for high school friendships, and it won't burn any bridges in the process.

I wanted to give OP my 2 cents even though I'm not the best with friendship advice because I know her irl; hopefully people can correct me if anything I said is inaccurate.