I don't have a video monitor, so I can't help you out there, but I do have a monitor that has given me reassurance that my son is safe in his crib, which resulted in me getting a better night's sleep.
I'm assuming your niece is looking into video monitors for the same reassurance...
The monitor I have is called "AngelCare" and it's made by BeBe Sounds. You can pick one up at Target.com with 2 hand sets for just $130.00.
This is a regular audio monitor that also has a movement sensor. The sensor pad is placed under the crib mattress. If baby doesn't move (and when I say "move" I really mean "breath" because the sensor is that sensitive) for 15 seconds, an alarm goes off. Nothing loud...just a steady tone that lets Mommy know that she needs to go check on baby.
When my son was about 2 weeks old he had to go into the hospital for a few days for periodic breathing (he'd stop breathing for about 5-7 seconds at a time, and he'd do it over and over again). The hospital sent us home with a heart monitor that had leads attached to a band that we had to keep straped around his chest. That blasted machine went off ALL THE TIME because he'd move and a lead would slip out of place...and this was a very LOUD alarm, so I'd end up shooting out of bed several times a night. I got so aggravated that I started searching online for any other options...that's when I found the AngelCare monitor and it was a saving grace!
I used this monitor for over two years with my son and it only sounded the alarm one time...when he learned to roll over and snuggled himself up against one of the corners and the sensor couldn't detect him. And we never had an issue with static interference like we did with our other monitor.
I have raved about this monitor to anyone that will listen! I highly recommend your niece checks it out. While video monitors are great for WATCHING baby, they still don't ensure that a sleeping baby is a breathing baby.