My gosh, it's too bad the .270 Winchester fell off the edge of the earth with the advent of the Creedmoor...it would have been perfect for this. Shoots a heck of a lot flatter than a Creedmoor and has less recoil than a PRC. It use to could be had for less than you'd spend on "spinning up" a new barrel in a superbly accurate package, such as Ruger American, or Browning AB3 (some of these had a 26" barrels!) A savvy handloader could run these up to 3150 - 3200 f/s without stretching the web with 130 grain Accubonds or similar. And the .270 is a HECK of alot easier to get to print sub-1/2MOA than the 3 or 4 Creedmoors and the 1 PRC I've had the pleasure of trying out.
If dad is dead set on a .264 bore and just needs an excuse to make a new barrel/rifle, then please consider the 6.5-.284 Norma above the 2 mentioned cartridges for this young lady. Shoots just as flat at hunting ranges as the 270, inherently easy to load accurately, and can achieve velocities equaling the 270 with less powder and 120-grain-ish bullets, which your daughter will thank you for in sparing her every little bit of recoil. Nothing wrong with the .25-06 and 115 grain Ballistic Silvertips, either. The bullet doesn'tvhave to be named Berger to kill something. 3200 fps in the 6.5-284 is easy with a 120 grain Ballistic Tip with good BC. 3250 is easy with a 24" 25-06 with the 115 gr BST, or 3200 with the 110gr Accubond. Both will kick much less than a PRC and shoot a heckbof a lot flatter AT NORMAL HUNTING RANGES (out to 500 yards) than ANY Creedmoor with ANY bullet you want to stuff down it's little throat. And the old 270 is MUCH flatter with it's 130gr bullet than ANY Creedmoor with ANY bullet out to 500yds...If you can find a 270 in the garbage dump somewhere after it was discarded with the introduction of the Creedmoor. MUCH higher quality brass available for any of these choices compared to the PRC. That is the framework and base of a super-accurate handload!! Something to consider!
True story: Big NW Nevada mulie succumbs to 120gr Ballistic Tip fired from a Savage 111 with 26" barrel and 1:8 twist with muzzle velocity of 3300 f/s at a distance of 200 yards on a slow run. Stumbled 2 steps on it's way to the ground with a center mass chest hit. (Yes, 3300 f/s was WAY too hot to be running that round, but the rifle liked it- Sub-1/2MOA groups @100, and obviously not too bad at 200. No recoil, but I had a factory brake and an 8.6 lb gun before Minox 50mm 15x 30mm scope.)
FYI, IF you decide to ignore good advice and build a Creedmoor, at least consider the 120gr Ballistic Tip. I have used it to drop large Southern 8pts in their tracks from an ultralight 6.5x47L with 20" barrel and muzzle velocity more like 2900. 270 130gr Ballistic Tip or BST or Accubond will do the same thing.
Best of luck to the lucky young lady!