What woman in the Bible had the most children and how many did she have?
I can find no mention of any particular woman having specific amounts of children in the earliest parts of the Bible. It often tells the firstborn's name and then goes on to say that they had other sons and daughters. For example, regarding Adam "After he begot Seth, the days of Adam were eight hundred years; and he had sons and daughters" (Genesis 5:4). How many children Eve had is unknown. The entire fifth chapter of Genesis is like that.
Abraham's second wife, Keturah, had six sons (Genesis 25:4), but we don't know if there were daughters or how many. Jacob's wife Leah had six sons and at least one daughter (Genesis 30). But Genesis 46:15 mentions the daughters of Leah, using the people named and the total count given, we conclude she had two daughters, which makes eight children.
Mary is mentioned having five sons (including Jesus) and multiple daughters, but we don't know how many daughters (Mark 6:3). So all we know is that she had at least seven children.
Job is mentioned having ten children (Job 1:2) and after losing them all he had an additional ten children (Job 42:13), but we can't be certain they were all born to the same wife. People do die and remarry, and sometimes men took multiple wives.
The problem is that often the sons are mentioned, but not the daughters. Even when a man's children are listed, we don't always know if they all came from the same wife or not since the wife isn't always named.