That makes absolutely no sense.  She is the breeder.....she knows it had to have been done between 3-5 days after birth.  I honestly am just shaking my head.  What did she possibly say her reasoning is for this "late" decision?  Also, if you put a deposit down on her and signed an agreement, this is YOUR dog and YOUR decision.  Not only that, a vet won't just dock a tail on a Yorkie because you want it done.  Let us know what happens.