I was actually thinking it would be a free action to reload if she paid the mana, or she could take a quick action to reload for no mana. It wouldn't be a quick spell though, so she couldn't do it with her quickcast. Basically she could shoot every other round if she didn't use her action for something else and didn't spend mana. If she spent the mana, she could shoot every round, but even though it has a mana cost (to reload) the attack still wouldn't be a spell, so she could only fire during her main action, but could take advantage of her ranged+1 trait. I don't think you actually would have to nerf it too hard beyond this, honestly, I think the standard 4 dice would be fine, although I was thinking it might be neat to give it fewer dice, but a decent chance at a poison effect, maybe 2 dice + d12: 8+=rot, or 0 dice (she'd actually roll one) and d12:6+= tainted. Like I say, some playtesting would be needed to balance this, so I mostly was interested in pitching the reloading mechanic.
Edit: I'm not married to the 2 mana price tag either, but I think it's important that she have the option shoot every round if she pays for it.