I'm with Zippy on this issue ....
But one point I'd like to make - is it isn't all about barrel length - at some point its about the gross weight of the gun as well - especially to a new shooter. I have O/U's in 20, 28ga and .410 that are around 7 1/2 lbs gross weight / with 30" barrels --- but they're too much for many young shooters. It isn't barrel length / its about their upper body strength and how the gun feels to them / so I picked up a Benelli 20ga semi-auto with a 28" barrel but its only a little over 6 lbs ....and new shooters like that lighter gun a lot more. Its weight isn't intimidating to them / and they just get more comfortable with it ...even though, as they get a little older or a little stronger they transition up to a 7 1/2 lb gun real quickly ....its better to start with a lighter gun if you can. But getting lighter / with a shorter barrel isn't very productive for follow-thru because the gun gets butt heavy and too "whippy" ...
Remember less weight in a gun means more recoil too - so when you go to a light gun, unless its a semi-auto you have to go to really light loads or it will defeat the purpose as well / and beat the new shooter up.
At 6'4" and 275 # myself - all of my field O/U's are 8 1/2 lb guns / with
30" barrels in 12, 20, 28ga ... and I use the same guns for Skeet and Sporting Clays. For Trap, I go even longer and heavier / because for Trap there is less Left to Right barrel movement -- so a heavier and longer gun helps smooth out my swing and follow-thru -- so I go to a 10 lb gun with 32" or 34" barrels ....but that gun feels like a big "sewer pipe" on a Skeet or Sporting Clays field ...
so all those things combined are how I approach this stuff ....but it just depends on what fits her --- and length of pull, drop at comb, drop at heel and gross weight for her will probably be different than what you want. Making sure she is comfortably fit is really important ....whether you buy used or new...
But one point I'd like to make - is it isn't all about barrel length - at some point its about the gross weight of the gun as well - especially to a new shooter. I have O/U's in 20, 28ga and .410 that are around 7 1/2 lbs gross weight / with 30" barrels --- but they're too much for many young shooters. It isn't barrel length / its about their upper body strength and how the gun feels to them / so I picked up a Benelli 20ga semi-auto with a 28" barrel but its only a little over 6 lbs ....and new shooters like that lighter gun a lot more. Its weight isn't intimidating to them / and they just get more comfortable with it ...even though, as they get a little older or a little stronger they transition up to a 7 1/2 lb gun real quickly ....its better to start with a lighter gun if you can. But getting lighter / with a shorter barrel isn't very productive for follow-thru because the gun gets butt heavy and too "whippy" ...
Remember less weight in a gun means more recoil too - so when you go to a light gun, unless its a semi-auto you have to go to really light loads or it will defeat the purpose as well / and beat the new shooter up.
At 6'4" and 275 # myself - all of my field O/U's are 8 1/2 lb guns / with
30" barrels in 12, 20, 28ga ... and I use the same guns for Skeet and Sporting Clays. For Trap, I go even longer and heavier / because for Trap there is less Left to Right barrel movement -- so a heavier and longer gun helps smooth out my swing and follow-thru -- so I go to a 10 lb gun with 32" or 34" barrels ....but that gun feels like a big "sewer pipe" on a Skeet or Sporting Clays field ...
so all those things combined are how I approach this stuff ....but it just depends on what fits her --- and length of pull, drop at comb, drop at heel and gross weight for her will probably be different than what you want. Making sure she is comfortably fit is really important ....whether you buy used or new...