Changing it to a shield wouldn't do much best option for that would be tweak covenant to mitigate physical as well as magical.

Selenes real issues cone from caress being on such song cooldown and dusk being useless.

So ideally what they need to do is slash the recast on caress make it more functional and then replace dusk with something different.

Maybe a mini contagion style thing. Reset dots /shadow flare. Or perhaps a small buff to direct hit rate or sonething