Accuracy is the biggest variable here. Can she hit a softball with it from 50 yards? You may want to consider a set of half way decent clamp on the rib fiber optic sights. They can be had for about $50. That will pretty much double effective hunting range of any smoothbore slug gun.

I think it will kill a deer dead as a door nail just so long as she can put the slug where it needs to go. Forget any illusions of a 200 yard slug gun here... but with a steady rest, some sights, and a little practice I think she should be able to take deer just fine out to 75 yards with it.

Practice, Practice, Practice, Practice.......... can't say that enough.