I had an amnio with my first child and a cvt with the second so experience of both and the miscarriage risk is really down to the experience of the person carrying it out. The more experienced I was told then the less chance of miscarriage.
But I know several people who have been in your daughters position and their babies were fine.
But, also other women have not had any further tests because they said it would not have affected their attidtude. If the baby is Downs they would still love it, they only thought it was worth having the further test if there was something they would do about it.
On the other hand I took the further tests both times because I wanted to know for definite, not a risk but a are they or arent they.
its up to your daughter to decide no matter what anyone else says.
good luck
F1x