Ysera is big and nice. And avoids Priest removals (watch out for Mind Control!) You want to have it by turn 9. But how often will that happen?
Let's say you will not draw any additional cards due to any mechanics, you will just get cards at the beginning of your turns. You are first player. By turn 9 you will have 18 cards left in your deck. Here is what calculator says about getting Ysera by 9th turn. Not bad!
There are some other things to keep in mind. By turn 9 you will probably get some additional card draws, this will increase your chance directly (lower "Cards left in deck" accordingly).
But you will certainly not keep Ysera in your starting hand, this technically reduces your chance to have her in your hand by turn 9, approximately by 3 draws.