Cap 1018: From weakest to strongest

Now that I didn't have any of my sisters' lives on my back and my part in this war against the Church of Light was over, I thought I might as well learn a little more about my sisters. 

I was surprised when Elizabeth talked about her birth, she was born directly from the Goddess while I was born from a puddle in a forest. 

"Now it's your turn, Natasha." (Elizabeth) 

"My birth was probably the only accidental one among us all." (Natasha) 

"You complain a lot, you've had the least problems." (Caitlyn) 

"You don't know anything, when you were born I had already participated in countless battles." (Natasha) 

"Stop fighting and you can continue your story, Natasha." (Elizabeth) 

I didn't understand what they mean by accidental birth, how could a Goddess have a daughter by accident? 

"Unlike Elizabeth, I wasn't born directly to our mother, I was born in the middle of a big war." (Natasha)