PLEASE DO NOT BREED FROM YOUR YORKIE!!! Until she is at least 2 years old! Yorkies need to mature properly and whilst she is still growing and maturing she needs all her energy going into herself!
Also ask yourself WHY you want to breed and what motivates you? If it's money forget it...to breed a decent litter and provide what might be very expensive Veterinary care you need an overdraft!!!
If you have a small Yorkie(there's no such thing as a miniature Yorkie in the UK KC Breed Standard) you may well kill her if you let her get pregnant!
There are far too many poor quality Yorkies and other breeds of dogs being bred in the UK...so many that rescue centres stand no chance of rehoming all the dogs and inevitably some get euthanased.
As you state in your post she is TOY sized(again there is no such size in the breed standard!) there are just Yorkshire terriers! Bitches should be 7 to 7 and a half pounds, they say this so that under size Yorkies are NOT bred from and put at risk! Males should be 3-4 pounds. Go to
http://www.thekennelclub.org.uk/item/199 to see the breed standard and have a re-think PLEASE!
all the best, Dawn