I think that there are different signs. I know that our mini Schnauzer was so "cuddly" and wanted to be held all the time when she went thru her first heat. (we had her spayed about 5 weeks later).
I don't think there is much you CAN do. Let nature take its course.... and keep her away from un-neutered little boys!
You may want to try a pantie if you are worried about "messes".
I am not sure, but I don't think that her heat cycle will interfere with having her spayed on the 11th....... but some of the more experienced breeders may be able to tell you that!
