She only got two years because it was a strong case of "diminished responsibility" and thus manslaughter, under s3 of the Homicide Act 1957, as amended (the amendment rewords the provision to give a more precise definition; Coroners and Justice Act 2009). It was not murder. The prosecution must have accepted the defence, since she pleaded guilty to manslaughter without a jury being asked to consider murder.
The Daily Mail has not bothered to explain this interesting and rather important matter, but the hints lie in the words that she lost control and in the background of her husband being alcoholic. She killed him when suffering a temporary disorder of the mind, brought on by extreme provocation over time, in effect. To suggest that this means she is a danger to the public at large is to ignore both the facts, which must have been accepted by the prosecution, and the law of the last 50 years plus.