I think the .260 will be easier to find than the 6.5x55 or the .257 roberts.

The 6.5x55 is available in a lot of old milsurps, but few modern rifles are chambered for it. Ammo is purposefully loaded weak for it because of all of the old rifles out there. In factory form the .260 will outperform it. Handloaded they're virtually identical.

The .257 roberts is a wonderful old round, but scarce as hen's teeth. You'll play heck finding ammo for it and even fewer rifles are chambered for it.

If I were picking a rifle a child or woman I'd probably narrow it down to the 7mm-08 or .260. I'd rule out the .243 because it's a marginal deer round to begin with. The 6.5x55 and .257 roberts are too obscure. Personally I'd go with the .260. The remington M7 rifles are chambered in the .260 and are correct in size for a smaller person.