Use the sleeping turns deliberately
The Matriarch begins asleep with Plating. Asleep ends when she loses HP or its timer expires. An attack absorbed entirely by Block does not satisfy the HP-loss condition, while passive damage that reaches HP can wake her even if the player did not select a direct attack.
Use the visible timer to choose setup that will affect the rest of the fight. Inflame supplies immediate Strength for later attacks. A recurring Power needs enough remaining turns to repay its cost. A defensive card that only provides Block this turn has little value while the boss is still showing Sleep, unless another effect makes playing it useful.
Awakening and the attack sequence
Once awake, the Matriarch uses Slash, Disembowel, an attack that also gains Block, and Soul Siphon. Her sleeping opening is conditional; do not assume the same numbered turn contains the same attack after a different wake-up.
Disembowel hits twice. Weak or a Strength reduction can affect each hit, while a single-use damage prevention effect may stop only one instance. Check the total intent after her Strength changes before deciding the previous amount of Block is still enough.
Avoid an ineffective early wake-up
A small passive hit can end the setup window while leaving almost all boss HP intact. Defect must account for the Lightning Orb supplied by Cracked Core; Poison and other automatic effects also make waiting different from passing an empty turn.
If the first hand cannot make productive setup, it may be reasonable to start damage sooner. The comparison is the value of the available sleeping turns against the attack that wakes her, not an obligation to wait until the timer ends. Bring a plan for repeatable output after those opening turns, because Plating and later defensive moves can absorb weak damage sequences.