I thought you were talking about me there! As a child I had thought processes all of my own just like you describe with the walking avoiding cracks and only on certain colour tiles. In the days of patterned carpets, I used to annoy a few family members as I tiptoed from floral swirl to green leaf! I can't remember all of them now because I think I grew out of them (I am normal, honest!) It might seem compulsive but I just liked doing it. I used to count tiles in the bathroom (still do that sometimes) including half tiles and part tiles (because of course, three part tiles make a whole tile!) and also how many knobs on the dresser drawers...it just filled up otherwise empty space in my thoughts-say if I was just doing nothing else. Maybe that sounds strange but it wasn't something I had to do, it was just something I sometimes did for fun. Well, it entertained me!
Your daughter sounds fine to me and as Bulldozer says if she is popular and has no interpersonal problems then it is just her little idiosyncracy. Of course, if she WAS obsessive and compulsive about it, then it's time to worry.
If she is popular amongst her peers, has no trouble forming relationships with others and you have had no concerns from the school I would be tempted to say to try and ignore these little idiosyncrasies (ex spelling). It could be some kind of control game that she is playing or it could be nothing at all. My advice would be to keep an eye on it obviously but don't bring attention to it.