She needs to see a genetic counsellor or a dr who understands the tests. First trimester screening (blood test and ultrasound) are screening tests, they are not diagnostic. They can not diagnose down syndrome. An ultrasound at 20 weeks can not diagnose down syndrome. Prenatally, either a cvs or amnio is needed for diagnosis of chromosomal variations.

I don't know your relationship, and whether your friend is open to information or whether she is just is need of support, but it sounds like she has been given misinformation (or that is what she has told you) and it is hard to make decisions if you have don't have the right info before you