Grandma Swamp does not appear directly in Plague of Shadows. Instead, she writes Plague Knight letters containing his miscellaneous statistics. They can be read by talking to the Mail Minion at the Potionarium. The minion always concludes that she is probably a witch.
In Specter of Torment, Grandma Swamp appears in the reflection of the Scrying Glass, located above the Magic Mirror room. She tells Specter Knight his statistics, but corrects him angrily when he mistakes her for a magic mirror when expressing his thanks.
"Grandma Swamp:Double, trouble, soil and shovel. My third eye knows your useless info! EXCAVATIO! The number of dig piles you've dug is [x]! AURUM INFINIOSA! The amount of gold you've collected is [x]! THANATO REFUTATUM! The number of times you've fallen in battle is [x]! TEMPORUM PERPETUA! The total time you've spent adventuring is [x]:[x]:[x]! I magically see all of your acts, come back again for more useful facts!"
"Shovel Knight:Thanks for helping me, kindly witch!"
"Scrying Glass:Brine, blight and fires bright. Your feats are laid bare to my all-knowing sight!. PARAPETIO ASCENSIUS! [x] is the number of walls you've scaled! MORBIDUM RETRONA! The number of times you've fallen in battle is [x]! CHRONOLOGICO! The total time you've spent adventuring is [x]:[x]:[x]! INCISIUM ANTECEDUM! The number of Dash Slashes you've done is [x]!"
"Specter Knight:Clearly, this is powerful sorcery... Thank you, bewitched mirror."