Make sure Penny has a bile acid test (BAT) before you reschedule her spay. Yorkies can have normal liver values (ALT) and still have an abnormal BAT.
All Yorkies should routinely have a BAT when they reach six months old as the breed is so prone to liver shunts. According to a study done by the U of Tenn, Yorkies are 36 times more likely to be born with a liver shunt than all other breeds combined.
There is lots of information about BAT on the YTCA website.
Health Committee