[quote=@Champion]...considering your bow generates the arrow itself, you'd be able to knock and release 4 times depending on how many arrows you fire each time.[/quote]
In that case I'll make it one Standard arrow to a knee for each of the three Undead Soldiers currently in sight.

Since we regenerate 10 points per post, and she's only looking to inconvenience the targets rather than kill them outright as well as aiming for quick firing rather than long charged shots, Arwyn will only channel 3 points of mana per shot, draining her of a total of 9 mana for this round of firing which will immediately regenerate again keeping her on 50 total MP.

Would that make her attack damage (Strength 4 x Weapon Power 3) = 12 Damage per successful attack? Or is it just Weapon Power 3 = 3 Damage per successful attack?

Once she sees how well, or how poorly, the attacks work the shadowbow will be able to tailor the strength of her shots appropriately. No need to drain herself completely with an opening barrage if only the bare minimum is needed to halt the creatures' advance.