There’s no concrete, canonical answer. I’d say you could justify your character still hearing the whispers, or not hearing them, whatever you want.
In WotLK, it was mentioned that Death Knights wear Saronite armor. Saronite being a metal borne from the blood of Yogg’Saron.
So… One could argue that the Void and undeath don’t get along too well. That being resurrected nullifies, or at least muffles, the Void’s constant whispers. They’d have less of an impact on her, or none at all.
However, you could also argue that Saronite was external, whereas the Void would have a direct line to her head. So, undeath might have prevented corruption from some contact with Saronite, but it’s just not strong enough to overcome the direct connection ren’dorei have with the Void.