Oh, I somehow realized while watching that I really enjoy Rachel being around.
Out of the reasons you named. And she really bonded with Lorelai, which was nice to see. I really loved these two together.
It's nice to see Rachel even realize that Luke and Lorelai have such a chemistry.
She knows at some point that Luke's heart belongs to Lorelai. Years before these two really do. And she makes a decision which I understand although I don't like the way she did it. Leaving him like that again
This broke my heart (although I haven't gotten there in my re-watch).
What else I loved was their talk in the storage room. I know it must have been difficult for Lorelai to kind of get Luke into Rachels arms but she did nevertheless. She only wanted the best for him.
Oh, and don't forget about the picture Rachel took of these two on that bench