Stale Mary has a little to say about her society. She and her zombies do peaceful jobs and care for the dead, the true dead, in the Halls of the Silent King. She tells of Hargrimm's worries about Soego and Acaste.
If asked why the Nameless One can understand her better than most zombies whose vocal chords are rotting away, then lets her touch him, he can learn the Stories-Bones-Tell ability, which allows him to speak to corpses. This grants 3750 XP.
With 16+ Charisma, the Nameless One can convince Stale Mary to reveal a path to the Silent King (grants 7500 XP). This is the only peaceful way to discover the Silent King's fate. She points the way to the northwestern alcove near her (X=420 Y=2620), where simply thinking of the Silent King opens a portal to his inner sanctum. (Charisma can temporarily be increased with the Friends spell.) This cannot be done if the Nameless One is already released from the Dead Nations.
If Morte has been kidnapped and you need a skull to trade to Lothar for him, and you have 16+ Charisma, you can tell Stale Mary of your predicament. She will offer you hers, saying removing it won't kill her because she's already dead. You can either accept and allow Stale Mary to remove her skull and give it to you, effectively "killing" her, or refuse and gain +1 towards your Good alignment count. There are plenty of other skulls you can trade Morte for, such as Soego's Skull, so unless you're actively avoiding having too Good an alignment, the second choice is preferable.