Don't be afraid to get your Yorkie spayed. Did you know that there are many benefits to getting her spayed like reducing her risk of cancer?
Spay and Neuter Health Benefits ~ Pawprints and Purrs, Inc.
If you had had her spayed before she ever had her first heat, her risk of cancer would have been zero. If you get her spayed before she has a second heat, her risk of cancer is still only 8%. If you wait until after she has her second heat, the risk rises to 25%.
Make sure and get pre op bloodwork done before her spay to alert your vet to any conditions that might make anesthesia risky. If her bloodwork is good, she'll be fine. Complications from pregnancy is much riskier than spaying.
Be very, very careful with her for the next few weeks. Males can smell a female in heat for miles away. They will be determined to get to her if there are any close.