Fallom was an hermaphrodite spacer (or descendant of) from planet Solaria. She is an infant, so she doesn't have the lobes developed yet. Bliss, by preference, uses 'her' and 'she' instead of their male counterparts.
When Janov Pelorat, Golan Trevize and Bliss; on their quest for Earth, get to Solaria, they meet her progenitor, Sarton Bander, who takes intererest on the humans, but then tries to kill them. Instead, Bliss kills him and scape of the planet, taking Fallom along after learning from authorities that, as there is a child excess, she'll be killed.
She goes along with them to Melpomenia, Alpha and Earth, where they learn that they had been manipulated by Daneel, who's brain was too complex to replace and failing, so he had to merge with an organic brain, Fallom's, because she had the lobes and, since she was a spacer, she lived longer that regular humans; so Daneel would live long enough to oversee Galaxia's creation.