I think it depends on the ultrasound clinic - it would probably be best to call ahead and ask. 

It might work as a way to reinforce to your daughter that there is going to be a new baby, though it might still be a bit abstract for her to understand based on seeing the ultrasound; at 19 weeks, the fetus doesn't look like what she probably expects a 'baby' to look like.

As an aside, we found several books on becoming a big brother/ sister that were quite helpful.  Our favourite was "I'm a Big Brother" by Joanna Cole.  There is a version of "I'm a Big Sister", as well as some potty training stories too.

Either way, it's probably not going to become "real" for your daughter until the baby has arrived and has been in the house for a while (and she realizes that baby is not leaving !).

Good luck !