No reason not to use the .270 if she shoots it OK. Unfortunately, "It don't bother me." is often wishful thinking. I know lots of big, tough, burly men who shoot 12ga "just fine" who also look like they got electrocuted if the gun says "CLICK!" instead of "BOOM!"
Most folks shoot guns with less recoil better than they do guns with more recoil.
Like I said though, anything if fine *if* the shooter genuinely shoots it without flinching. I find most folks flinch a lot more than they think and with guns with a lot less recoil than they think.
If she's good with the .270, great, but it won't do anything the .243 won't do. A bad shot with the .243 won't be a good one with the .270, or any other gun.
As for "long shots" with the .243.... it's got plenty of oomph...
Still happily answering to the call-sign Peetza.
The problem, as you so eloquently put it, is choice.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.