Who is Manella Dubanqua Seldon from Forward the Foundation and what is their importance?

Manella Dubanqua Seldon is a tall, attractive prostitute who shows interest in Raych Seldon in a bar in Wye Sector on the planet Trantor, while he is working undercover for his father, First Minister Hari Seldon, Manella helps Raych, who calls himself Planch, infiltrate the rebellious Joranumite movement. They fall in love but are ordered apart just before infiltration into the Palace grounds to assassinate Hari. Disguised as a gardener, Manella shoots dead Gleb Andorin, the man assigned to silence Raych by killing him, and reveals that she is undercover security. Forced to retire, she soon marries Raych, whose mother Dors Venabili accepts her only on her own deathbed. Manella and younger daughter Bellis accompany Raych to the planet Santanni, where civil war breaks out and they are presumed lost when all trace of the Arcadia VII is lost.