Stacey Newkirk-Smalls, 42, of Tacony, Pa., was convicted and sentenced Monday after a one-day non-jury trial by Common Pleas Judge Jeffrey Minehart.
Under Pennsylvania law a second murder conviction automatically results in a life sentence without parole. She was given a 20- to 40-year term on the first count.
Prosecutors argued Newkirk-Smalls poisoned the twins, Adam and Eve, before drowning one and suffocating the other inside the home she shared with her husband, the children's father.
Family and friends told the Philadelphia Daily News they remained supportive of Newkirk-Smalls, a former nurse, because they believe she snapped when she learned her husband was having an affair with her adult daughter.
"She loved her children dearly. Whenever you saw her, she was talking about the children, she was smiling at them. She had nothing but good things to say. But what happens when an ultimate betrayal happens?" asked C. Chekejai Coley, one of Newkirk-Smalls' best friends.