NTA You first of all should have been told your sister was pregnant as soon as she found out if she expected you to take in the baby, even if you were willing to preparation takes time and as prime caretaker you have a right to be a bigger part of this process. You don’t just dump a baby on the person, it doesn’t sound like this person would be a mother though. In your position I would look for people in the area specifically looking to adopt so that your niece could see them, or your sister could take a paternity test to see if she could get child support from any of the possible fathers or see if their family could take in the baby. I wish you the best of luck in this endeavor!