The Ant Matriarch is good at one thing: making more ants. If you can keep her alive long enough to pump out several sets of ant pseudocards, you can use an Orb of Unity to potentially deal a killing blow to your opponent. It can be a fun card to play, but the Matriarch can also be easy to shut down by ally removal or burn type cards if you have nothing to prevent them. Playing the Matriarch together with an Ant Colony or two makes it a lot sturdier, and in turn makes the ant pseudocards stronger.
Strong against: Slow-developing and quality decks.
Weak against: Ally removal cards, burn decks.