Wont make that much difference, but an inch of barrel is probably an ounce. Leave the barrel alone, she is growing every day. You will want those inches back
I'd put it in the youth stock and try it as-is for a while, to see if the extra few inches are too cumbersome. If so, I'd maybe cut back to 19-20" to preserve balance. My 7yr old hunted with a 20" barreled 700 7mm-08 and it was plenty compact, even in a box blind. My other daughter is getting a 22" 700 .260 for Christmas, and we'll see how it goes in a youth stock, but I'm going to try it out before cutting it back any shorter. There may be no need to chop it.
