The milling doesn't matter because, like others said, it's like not being able to draw the cards from the deck in the first place so in any other random black deck it doesn't matter that you milled away a bit of your deck.
In a dedicated deck it actually even helps that you milled extra cards since you want them in there.
Think of it like this: In any random black deck she is a +1 bonus and fetches your creature back to your hand and in a dedicated graveyard deck she is a +2 or more.
It isn't really a downside that you mill away the cards because you might as well have not seen them cards anyway. The only difference is your visual bias of actually seeing the cards you didn't get to play but in actual fact that is no different than looking through your deck at the end of a game to see what cards you might've drawn.
The difference is obvious if you have any idea how to think of randomly distributed decks of cards. The odds of having any given card at the bottom of your deck are unchanged, and they are compounded with the completely separate odds of milling that card away, resulting in greater odds that any given card will be rendered useless. It's only the same thing as not drawing a card if you think of "luck" of the draw, instead of thinking in terms of probability.
Granted, there's also the fact that she digs and may reach cards that would have been out of drawing range otherwise, but that's pretty negligible unless she lives for 5 or 6 turns.
Self-milling cards are terrible outside of dedicated self-milling strategies, I thought that much was obvious. Maybe the tradeoff is worth it... in the late game, where you might just as well use more powerful effects. It's not like you're going to -2 her a bunch of times.
And, Zombies and MBC are going to be some of the first things I try and she'll be in them. I just don't have much faith, is all. I'll happily eat my hat if I'm wrong.
Now, can we please drop this topic already?