Natural Guardian

Of course she is biological mother and natural guardian.

The biological mother automatically replaces the biological father as natural guardian to the minor child upon the death of biological father of the child 

If mother is remarried the grand parents may challenge custody of grand child as she and her new husband may neglect child, approach civil court on gaurdians and wards act so now mother is not natural gaurdian as she has remarried. The court will decide.

Character of biological parents never change they always remain natural guardian of child even they get married  again..

Even though the mother get remarried she is natural guardian of her minor child, remarriage didn't lose her right of guardianship.

The mother's remarriage will not disqualify her from becoming the natural guardian to her biological child after the death of her husband.

She is the only person hving full rights as a natural guardian to her biological child after her husband's death, whether she remarries susbequently or not 

If she is hindu ceases her religion she looses her natural gaurdianship,.

Even if mother changes her religion or remarries she will continue to be natural guardian of her minor child.

What is the context for this query? The posting suggests deeper issues.