Edriss seems to be identified mostly as female (and identifies herself as a mother, which is a gender-specific term). Eva calls her female, and Eva's probably the one that knows best. So I tend to go with Edriss being female.
But like, Yeerk gender is a whole can of worms.
Not to be all 'citations!', but:
"“She has a reason,” Eva said.
“Tell me.”
“She has children.”"
"<I shouldn’t have helped you,> she said. <Even if it did lead to open war, I shouldn’t have helped you. You filthy, evil thing. I thought I’d found something decent inside you. I thought you were a mother, too.>
<I was. I am.>"
"But someday she would know me. I would tell her all about me, all about who I was, how she had come to exist. And she would love me, as a daughter loves a mother."