I use a .308 for elk hunting and don't have too much to add, really. I killed two this year using a 180gr Barnes XLC over 44gr of 748. It's not made any more, but the TSX will do the same thing. One took a lot of punishment before it went down, but the other crumpled and slid 10 yards to a stop after the herd was running full speed away from the pushers. Shot placement is key. I don't know what kind of terrain she'll be hunting, but where I hunt in Idaho, there are lots of trees, and shots over 100 yards are rare. These are elk, after all, and are usually moving, often hauling ass. Better to teach her how to shoot a moving target at close/mid range than spend a lot of time at a bench rest if it's anything like where I hunt.
At the ranges we shoot elk, (sorry - 'harvest') I have not noticed any difference in how they die when being shot with 7mm mag or 300 Win, compared to my 'lil 'ole .308.
Also, teach her to work the action quickly for quick follow-up shots. The short action is a plus for this.
In my experience, lung shots work quicker than heart shots on elk, but being greedy and trying for both is best. Again, keep her practicing, it's more important than any bullet or caliber. Still....
I like Barnes, Partitions, Swift A Frames and Fail Safes for elk. 180gr bullets work great. I may try the 220gr Partition next year, though.
Tom