Though Eris's own sexual desires could be said to be strong, when seeing Lucy or the pregnant Roxy, she might be thinking that she got a late start.
In the Asura Kingdom, to no small extent the perception was that to properly call yourself a wife, you had to give birth to children.
I didn't know what Eris thought of that, but if bringing forth a child will make her relieved, then I wanted to allow her to feel relieved soon.