2 moms question

How can you call a person a 'mom' when they walk away from their child? This biological 'mom' walked away from her daughter twice! Once at 6 months and again at 5 years. How can a 'mom' walk away from their child twice! Live in the same town, had regular visitations; to say that they "give up" and walk away! How is this a 'mom'?? Someone explain this to me cause as a mom I don't understand! How can you walk away from your oldest child and another child still at home? *I feel my daughters adoption was different then most other adoptions and this is not reffering to any other bio'mom' than the one of my daughter*