ultrasound shows swelling around the neck?

Hi,
Welcome to the forum. I am really glad to help you out. The test that your step daughter has undergone is called nuchal translucency test. The nuchal translucency (also spelled nucal translucency) is a collection of fluid beneath the fetal skin in the region of the fetal neck and this is present and seen in all fetuses in early pregnancy.

The fluid collection is however increased in many fetuses with Down's syndrome and many other chromosomal abnormalities. It is called a 'translucency' because on ultrasound this appears as a black space beneath the fetal skin. The nuchal translucency test also checks whether the baby has a visible nasal bone.

It has been seen that approximately 3 in 4 babies with Down's syndrome do not have a visible nasal bone at the time of the first trimester screening test. If the nasal bone is visible at the scan then this reduces the chances of the baby having Down's syndrome.
I suggest you to get an evaluation done from a gynecologist.

I sincerely hope that helps. Take care.