Welcome to the site!

I am not sure which countries have a ban on semi auto's (personally dont use them) but a 300 Mag will be more then sufficient for any Plains Game you will encounter. Just make sure your daughter can shoot it well. If the recoil bothers her I would go with a 30-06 or maybe a 270 if she is a good shot.

Safety.... For the kind of hunt you are looking at I would think SA and Namibia would be the better options. I have never been to Namibia but have been to SA many, many times and never had a problem. It is like anywhere else. Use your head on when/where you walk around and you will be fine. SA is a beautiful country and it gets a bad rap as far as crime/danger is concerned (obviously, there are bad spots like anywhere else in the world. Use some common sense and you will not likely have a problem). There is lots to see. If you don't want to see the sights then likely your operator will pick you up from the airport and take you to the lodge/camp, then take you back to the airport when you are finished.

Youth hunts... While I personally dont know of an outfitter that offers special youth hunts (never asked), I am sure they are out there. Ask for references with younger children and see how the hunt went, if the PH was good with them and if the younger hunters had a good time. I am sure you wont have a problem finding a good outfitter/PH. There are a few on this site with very good reputations.

I think 5 days of hunting would be plenty of time to take two trophy animals.

More advice;

Join The Hunting Report and use it as a tool to check out potential outfitters. Get her out on the range and hunting as much as possible between now and then. If you are going to buy a new rifle/scope, do it early so she can practice with it for as long as possible. Have Fun and Good Luck!