Deadzone is not completely ground-based like Damba's gourd or Tyra's fire. It works like Viktor's ult which means that it can be blocked with shields as long as you're not exposed to the middle.
As a support, be wary of Dead Zone! Do not stand inside it unless it's unavoidable and do not attempt to use healing abilities on allies affected by it until they've been cleansed. Remember that the effect lasts for 2 seconds after exiting.
Most of Willo's kit relies on area denial. After Seedling or Dead Zone have been used, it's better to stay out of reach. Remember that she has quite a large cooldown for those abilities!