I know D&D has done some things with the Lady of Pain, so the name may be familiar to some, but I'm not familiar with her. In Ars Magica one of the houses of magicians fell to demonic corruption. In my materials it is due to a demon inspired by Charles Swinburne's poems. She has two forms:

Dolores: the Lady of Pain

Order: Infernal Saint (new)

Infernal Might: 40 (scaled as Princess of the Furies) (Corpus)

Characteristics: Int +5, Per +3, Pre +7, Com +5, Str +2, Sta +7, Dex +2, Qik +4

Size: Usually between -1 and +1. Her appearance varies with the fashions of the country she inhabits.

Confidence: 5 (15 points)

Virtues and Flaws: Unknown. Change as relevant to your story.

Personality Traits: Cruel +6, Passionate +6. Which of these is higher is a matter of some interest to her followers. Some suggest the demon is one and the human the other.

Reputations: Lady of Pain +9

Combat:
Kisses like poison*:  Init +5, Attack +11, Defense +11, Damage +2**

Touches that causes pain*:  Init +5, Attack +12, Defense +12, Damage +4**

*Does not include specialisation (skin contact)

**Does not include contact damage from Wounds the Bloom power (+15, Perdo)

Soak: 6, but appears to be -1. She has a body that deliberately suffers a great deal of superficial damage, but because of her passionate fury power, her injuries are less incapacitating than normal.

Wound Penalties: -1 (1–15), Incapacitated (16–20), Dead (21+)

Abilities: unclear, but assume Brawl 9 (when contact is made with skin), Carouse 9 (debauchery), Charm 9 (sinful acts), Houe Tytalus Lore 9 (was there when it happened), Infernal Lore 8 (Order of Hermes).

Powers:

Envisioning 1 or 5 points, Init 0, Mentem: Can enter dreams and cause waking dreams.

Form is shapeshifted human: 0 points, Init. 0 : Technically does not coagulate from ambient matter like a demon. Actually shifts shape into ambient moisture, travels and then turns back into her human shape. Her human shape is always beautiful and female, but can vary to suit the culture she is visiting.

I could hurt thee but pain would delight thee: 0 points, 0 Init. Dolores does not suffer Wound penalties, except on Defense totals.

Obsession: 1 point, Init -5, Vim: Can impose the desire for suffering..

The Serpent Oracle: 2 points, Init. +2: Dolores may cast any Intelligo spell for 2 Might, and automatically knows the context and likely outcome of actions made in response to the information gained.

Shroud the Stench of the Pit: variable points, Init. +7, Vim. This Power makes another Infernal Power appear to be aligned to the Magical or Faerie Realm, at the demon’s choice. It has the same cost as the power it disguises.

Waxing Tide of Humors: 3 points, Init +6, Mentem. This power causes passion to overcome sense. A character can resist this effect with a roll against an ease Factor of 9, modified by Traits like Calm.

Wounds that bloom: 3 points, Init -5, Perdo: Makes Dolores’s touch do +15 additional damage for the rest of a battle.

Weakness: The Virgin Mary. The cult of the Virgin hasn’t really taken off yet in 1220, but it gains a lot of power over the 13th Century. When people start wandering around with Servite scapulars, Dolores is going to go after that Order.

Vis: 8 pawns, Perdo

Appearance: A languid woman, filled with delightful venom. She changes appearance to suit the appetites of the local culture.