The person who can best answer this is your Dr.
Personally, I would still go to the playdate.
with a google search I found this....
With this in mind, realize then that it is extremely rare for someone who gets the vaccine virus to spread it to another individual who does not have any protection against chickenpox. In fact, there are only three documented cases of chickenpox out of more than 15 million doses of vaccine given to date that were transmitted to healthy people from recently vaccinated people. These three cases ended up being mild disease and there were no complications. More importantly, this type of spread has only been documented when the person receiving the vaccine develops a chickenpox-like rash right after their shot.
http://life.familyeducation.com/illness/disease-preventio...