is pneumonia catchy?

Long story short, my niece was diagnosed with pneumonia three or four days ago. All of a sudden, my DD who has had a cold for two  has developed a wicked cough going into last night and into this morning is coughing quite a bit.  We had her humidifier going and vicks on her chest before bed.  The kicker is we are having DD's birthday party today!  Do you if know is pneumonia catchy?  Also, I am wondering if I should cancel party so I don't get other people sick... My pedi's office doesn't open until 8:30 so I will call them to ask for advice but just curious if any of you had experience with this.  Thanks!!