awww hugs hun- it will get better
if give her a couple more days and if she is still saying that she has no friends- then just mention something to her teacher- she can make sure she is ok at lunch time etc.
btw i am positive they do prep/grade 6 buddies at your DD school- i am sure they will do that soon and she will be fine.
btw my friends little girl started in prep at your DD school this year as well. If you want i can get you guys in touch with each other and maybe organise a play after school or something to kick along a friendship. She is ace my friend and really easy going!!!
let me know if you want her details and i can give her the heads up!!!
mwah