Rhiada

 is the receptionist of the Silver-Blood Treasury House in Markarth.

There's a quest to talk to Thonar. After she greets you and you persuade her to let you talk to him, the first dialogue you pick with him (any of the 3) sets off the 2 undercover NPC's and Rhiada gets killed by them unless you stop them in time. Be careful not to hurt her or Thonar in the fight against Nana Ildene and Donnel that turn into sorcerers though, or the guards will come.

Rhiada is married to Eltrys and is a patron of the Silver-Bloods. If she lives through the attack, Thonar will flirt with her asking about her relationship. This may be a plot to assassinate her spouse in order to have her as his new bride.