Thanks everyone!
Well, I have to say she is a very good protector indeed! All worked out in the end, but it was a bit of an adventure... It was amazing to see my super sweet girl in action - wow!!!
My coop has indeed an area underneath (well, I was not as smart as mailmamm here!) and... of course that's where they set up for the night.... so I had to take them out of there because I did not trust that a predator would not get them...
My poor ("mostly innocent") dog was walking nearby and "got it" from momma-hen when I reached out for the chick!!! (I tried to get momma, but could not, so I figured the chick would make momma come out... it did indeed!! Yikes!!) Lots of exasperated yells from everyone (chicks, momma, myself and dog!!) later and I managed to put the chick I had in my hand in the coop, got momma in the coop too, but the second chick was then still under it looking for momma... It could hear her calling above and actually, finally, it made it up the ramp!!!
The good news is that they immediately went to the nest box where they are nice and cozy!
(Someone in the thread asked why I cared if they were in the nest box or anywhere else in the coop: my coop is pretty full, so the floor gets dirty quickly from the perches above. I am happy they can be at the box where it's cleaner and nobody will poop over them!! Yikes!)
So, at this point I would say that in the future I would be VERY comfortable with momma taking care of the babies even from hatch, EXCEPT for the fact that they may have trouble going back into the coop if you have a raised one with ramp and you better have a plan B to get them in... (unlike me!!)
My coop has a ramp only on the outside (the whole coop sits about 18".) I am hoping that after they come out tomorrow, everyone may learn how to go back in... I don't really have a way to block under the coop at this point... but I will at least put the dog away tomorrow before intervening...!!
Hopefully a last question: when do they normally become independent from momma??