and as the resulting questline in
Heavensward that resolved the whole situation mentioned, everything happened so fast we didn't even get the chance to even confirm she really
was dead - given the fact we had barely risen from our seat when Teledji and the Brass Blades burst into the room and promptly arrested us before we could check Nanamo for any sign of life (this was also why Ilberd bared Raubahn from seeing Nanamo's body - that would have blown the whole scam). The substance used on Nanamo merely needed to put her into a deep long-term slumber that could be mistaken for death on a cursory examination - the ALC Guild was clearly invloved so it would have been relatively easy for them to come up with such a potion.
And remember, the staged assassination was really all just a means to an end - an extended
Batman Gambit designed by Lolorito to eliminate Teledji without having any suspicion falling back on him - having our reputation destroyed and the Scions scattered was 'collateral damage' to him