There have always been people who act in ways that lie utterly outside the bounds of other people's comprehension. That does not make them insane.
LL knew that killing babies is murder and an action outside the bounds of the society she lived in. She knew that, and then chose to do it. There are always people who will choose to do things because they are forbidden, and the greatest forbidden act is to kill someone. We attache a special horror to killing the defenceless - like small babies, but killing is killing, whether babies, children adults or old people. Hers was a conscious choice.
I can see no alternative to a whole life tarrif prison sentence. She is not safe to be allowed to live with other people.
As for Munchausens Syndrome by proxy. This was identified by the paediatrician Sir Roy Meadow in 1977, he has since been discredited when several women served prison sentences for killing their babies when they had successive cot deaths. Meadows Law stated that "one sudden infant death is a tragedy, two is suspicious and three is murder, unless proven otherwise".