First of all, let me say, this is just an idea of how I would do it. I am not a silver smith! But I have done silver jewelry, back in the early seventies, when I was a Dental lab tech. I made conchos, crosses, animals,and turquoise jewelry. Haven't done any since. But not knowing what you want to put in an open backed bezel, it is hard to get an idea about what steps to take. Again, I am NOT a silver smith. Once something is soldered, the solder, will take a higher temp. to melt, than when it was first soldered. So if you want to solder something next to something that was soldered, you can do it without melting the previous solder point. But you have to be careful as to how much heat you apply, and for how long. I hope this helps, but it is probably something she already knows. Keep searching for silver working, making silver jewelry, tips for making silver jewelry, etc. just keep searching, and changing the wording. Something will turn up.
What is going to go in the bezel? You can use sheet silver, and either cut out a piece in the shape you want, and form it to fit the piece you want in it, and then use a jewelers saw to cut the back out, or you can cut an appropriate sized strip and form it to the shape of the object you are putting in the bezel, and cut the overlapping piece off, and then remove the object, and silver solder the strip. If you are going to bend the top part of the bezel over, you can do that either before, or after you have the object in the bezel.
Or you can do that to fit, and then cut the corners to bend, and then remove the bezel, and solder the joints, or cut them in a decorative style. Being a dental lab tech, I would sometimes just make the piece in wax, and then cast it, and do final fitting, afterward. Wish I could be more helpful.
Wayne