I picked up an older Marlin 15YN at a gun show last year for around $75 I think. It shoots great and fits my 7 yr old like a glove. No trouble with him getting bored with the single shot yet but he's only been out with it a couple of times so far so it's still new to him. I think more than the rifle, it's the targets they get bored with. Pick up some sort of reactive targets and it'll hold their interest a bit longer. I think the Marlin 915Y would be a great gun for her and she'll be able to teach her kids to shoot with it.