Sierra Nelson’s now 3-year-old daughter Ava cannot sit up by herself.The little girl can’t walk, either, and she must be fed through a tube.That, Chief Deputy District Attorney Sean McCormack said, is because of the severe brain injuries and 39 bone fractures inflicted on Ava by her mom.Ava, in short, cannot live like a normal 3-year-old, and will be afflicted with disabilities for the rest of her life, the prosecutor said.On Tuesday, Dauphin County Judge Deborah E. Curcillo ensured Nelson’s life will change for the worse as well. She ordered the Harrisburg woman to serve 7 to 17 years in state prison on the aggravated assault and child endangerment convictions a county jury handed down against the 26-year-old last month.“That child…put her trust in you,” Curcillo told Nelson. “And you violated every duty that could possibly be given to a mother.”Investigators said the then 4-month-old Ava was found to have sustained severe brain trauma, 33 rib fractures, four skull fractures and a fractured clavicle and vertebrae when she was rushed to the hospital in March 2016. She was also severely under-weight, McCormack said.Nelson consistently blamed the child’s father, Andre Houston, for the infant’s injuries. Houston pleaded guilty to a child…