Requiring the reanimated permanents to be milled cuts away the strongest reanimator starts that involve tutors like Entomb and Buried Alive, but it also makes the entire combo more manageable because you only need to find a mill engine rather than a bunch of disparate cards
Second, she can immediately tutor for either a perfect answer or a nasty problem that perfectly matches the board
The first is cards with madness, such as Big Game Hunter, so when you discard them, they can still be cast
For now it is going to live and die on the back of this Selesnya shell being well-positioned and not running into Extinction Event or Ugin, the Spirit Dragon, but it does a lot to help this deck do the truly overwhelming things it needs to be a contender
This format has a lot of Artifacts including Artifact creatures, so a card that can destroy them for one mana is already a card youll always play