My brother has a Ruger M77 international with a 18.5 inch barrel chambered for the .250 Savage. We have had many
first time shooters, man and women, use this gun. It is very low recoil and has enough power to take deer out to 150
yards cleanly. I think any rifle in a caliber such as the .250 Savage, .257 Roberts, .243, and the .260 would be a good choice.
Most importantly is that the gun fits her and she is tought good technique from the start. With good technique she could
learn to handle that .300 of yours.