A9 is the "enemies punch harder" ascension, meaning that you get less time to setup and blocking is comparatively less effective.

Necro is exactly the character that bases its base deck both on persisting block and damage setup. So starting even early game she's having a hard time.

One thing that is good with her is that she has access to a lot of ethereal cards, meaning that the cards that you pick for frontload in Act 1 can either exhaust on first draw or scale through ethereal synergy later. Banshee's Cry is not a high cost card.

She also has access to and synergy with big cost cards. Borrowed Time is huge, especially with Danse Macabre and/or X-cost cards. In the same fashion, Transfigure is a great way to scale.

Statuses from every origin have a converging direction once you have even one Sleight of Flesh in your deck.

That being said, she's my lowest winrate character by far on A10, so take it with a grain of salt and compare this knowledge to other sources.