It is explained that Niobe was originally Morpheus’ partner, before he got caught up in the prophecy of “The One”. She then moved on to Commander Lock, though it is fairly obvious she still holds a flame for Morpheus and when needed, she’s there by his side.

Niobe is a stereotype.  A skilled and very capable woman attracted to powerful and influential leaders, they make a good team. She believes in him, but not enough to stay by his side when he stops giving her the attention she needs, in order to pursue his goals.