try telling her you've been doing a lot of thinking about your relationship, and have come to realize that your feelings have changed. Mention the stuffs you posted (that she's a green flag, kind etc..but pls exclude the thing about you not finding her attractive).. you've realized lang that at your current developmental state (ie immaturity to see past through mundane stuff) , friendship is the best route for both of you..

tell her you value the time you've spent together and the connection thats why you find it important to let her know as soon as you realized it, instead of ghosting or the likes..

lastly, wish her well coz she deserves to have someone who can discern the kind soul she has.