Dallah Thaun is an aspect of Yondalla that first appeared on Races of the Wild.
Some extracts from the book:
Dallah Thaun, the Lady of Mystery, is the dark aspect of Yondalla. Physically split off from Yondalla when she created the halfling race, Dallah Thaun is worshiped both as a deity in her own right and also as part of Yondalla.
For example, when someone evil harms a great number of halflings, Yondalla’s followers nurture the survivors while Dallah Thaun’s seek vengeance.
Should any dirty work need to be done, it falls under Dallah Thaun’s purview, and Dallah Thaun is said to receive the souls of dead halflings and guide them to their final reward.
“Don’t get caught” is her credo, and the lesson that she passes along to all her worshipers. Dallah Thaun also serves as an avenger for any wrongs done to her people.
She's the halfling goddess of secrets, wealth, and thieves.
Link to the Forgotten Realms wiki with more information about her: https://forgottenrealms.fandom.com/wiki/Dallah_Thaun
I would suggest Trickery and Deceit as her first aspect and War and Destruction as her second.
While apparently she might not be canon in FR (or is she? I'm not sure how it works) neither are canon for FR deities such as the Sequence, Mother, or the Drowning Man, that actually are eligible as deities for our characters.
She would fit a niche for chaotic halfling characters similar to the one Arvoreen holds for lawful halfling characters right now.