Blood clots in lungs?

CD
One of my 6 sisters just called me to tell me that another one of our sisters is in the hospital with 20 blood clots in her lungs. I  freaking out I am so worried for her. She is only 33 years old and very healthy. Anyone out there have experience with this? Luckily she is a nurse so she knew something wasn't right. Any advice or reassurance would be welcomed !