Many new shooters tend to stagger their stance too much. Especially those who don't have as much upper body strength. I've seen this with smaller guys too. Have them square up and have them think leaning forward a bit into the rifle. It will give them better balance and put the stock squarely into their shoulder rather than sliding up. It also tends to help them bend their knees a bit rather than the straight up and down form you often see. When they do an overly staggered stance it puts the majority of the weight on the back leg especially near the heel. When they square up they feel more like falling forward but of course they aren't and this helps with recoil. Should help, but you have to keep an eye on them, they will quickly try to revert back to the overly staggered stance and leaning back due to the weight of the rifle. It's natural to try and make it easier to balance the rifle. They don't realize what they are doing is actually making it harder for them.
Cool video. Looks like she had fun.
From matt308's lill lady :
when I first started shooting I would stand straight feet practially together and lean back. My body would really feel the recoil and shoulder would hurt for days after. I learned after the shotgun test here try this, birdshot, birdshot, buckshot, birdshot, slug. Then also with the m14. which honestly i am pint sized as most people would call me so it's not my firearm of chose.
With thousands of rounds down the barrell of the 22lr I am teaching myself to get of that nasty habit almost every girl you see on youtube shooting a firearm.
I now find myself standing with my left foot out infront of me, upper body pushed into the buttstock (to absorb that 44mag recoil

knee slightly bent arms tucked in under the gun to support it more not like chicken wings everywhere..
I am starting to learn a new sitting position so i can balance everything out while getting good with this new rifle i picked up.
but yes I do start to lean after x number of shots. Due to the weight of the gun possible? yes.. or I haven't noticed myself moving out of the correct position until I get told. Main thing is practice practice practice is what i am told. and you will get better at it!
Oh yeah boobs do get in the way at time

, just thought i point that one out!
TO THE OP:
Good Job on getting your friend out shooting!! very proud! the rfb looked to kick her pretty good!
now if only I could get my girl friends and sister to come out shooting !