I don’t think it would be an issue with her being overpowered while in her desecration zone, but I think she should not have as much power outside of it. The shield should stun inside the zone. Outside, have it slow and silence. Have all her toys in the zone, but just have her be a competent defender outside of it. I think people wouldn’t mind that. That being said, I think her desecrate zone should be a black fire, and have an effect of black flame around the peripheral of the characters when they are in it. Make it known that you are about to get hurt if you don’t leave, as is, I think it’s not as noticeable as it should be.
They could possibly make it an ult that stays in a large area (like the middle of the sentry area), and have it last indefinitely until she recasts her ult or dies. However, it stays in one place, and doesn’t move around, hence the extra large area.
Her helix could also add to her desecrate while upgrading other abilities as well. Like you’re building your own death zone, customized just for you. Last, for the ult upgrade, I think doubling its radius or having follow at tenth speed would be good options.