I like the caliber choices of 7mm/08, 308, or 30/06, any of these with proper bullets are fine out to 300 yards IMO.
As far as a heavy gun for help with recoil, I'm iffy on that. My daughter struggled with holding a heavy gun in the free hand position, her arm holding the foregrip would tire very quickly. You know how many times that you have to hold a gun in the ready position for a bit before the animal turns just right. A semi-auto along with a nice recoil pad will do her fine I think, I'd try to target 8#'s or so. And I'd also consider the added weight of a set of bipods on her gun, I doubt I need to say how valuable it is to have a steady rest when your heart is crashing with excitement. I have a couple sets that extend clear out to 30", so they can be used from a sitting position in most cases. My daughter has shot all her deer to date off a bipod...and has gotten all of them that she shot at except one.