A gravid uterus
is a uterus during pregnancy
, just thought you should know that.
Cardiac activity means that the baby's heart beating, this isnt visualized because the baby's heart is only formed by the 6th week of pregnancy.
A well defined fetal pole
is also a good thing, because it means there is no miscarriage
As such as far as I can tell there is no problem with your sister's pregnancy at the moment.
And yes you can relax till her next ultrasound
Also if there was a problem, the doctor would've told you the problem right there and then, so dont worry. I am assuming this is the first pregnancy in the family, hence you are so worried and stressed. Just relax and tell your sister to relax and enjoy her pregnancy.
I hope this helped.