Angela Lee, 46, denied murdering Danielle Firth, claiming the baby fell on a plastic castle before changing her story to say she accidentally dropped her on her head.
But a post-mortem examination found five separate areas of bruising to the child's face, including her left eyebrow, ear, nose and jaw line.
Sentencing Lee, of Denby Dale, West Yorkshire, the Recorder of Leeds, Judge Brian Walsh, said Danielle's death was "a tragedy on a wide scale". He was satisfied that Lee had, to some extent, a fragile temperament. But he added: "For some reason on the day of her death, and I accept for a very short period of time, you lost your patience and self control probably while you were attempting to feed her, and in frustration you slapped her, shook her and dropped her."
Lee, who had been a registered childminder with Kirklees council since 1988, had been looking after Danielle for 10 days when she died on 12 February 1996.
During the trial, Lee claimed that she dropped Danielle head first as she tried to reach a box of tissues to wipe the child's face. She put her down to sleep and called an ambulance 45 minutes later after finding her "pale and floppy".
She said she was too frightened to tell the truth about dropping the baby because it would be seen as negligent and she could lose her childminder's licence.