IN my mind, too many gadgets, either get her one of her own, or just cut the one down to fit her, Its easy to use a one inch or so shorter stock. A five foot person can handle a 870 with a youth stock, as can a 6.5 footer.

In the crash of the night, fumbling with an adjustable stock does not seem like a good idea, If you need it, it should be already pointed at the threat, not while you try to see which adjustment slot the latch is in.