I know where Jessica Townsend got the name 'Morrigan Crow' from!!! Well, part of it anyway.
So, I was looking up nicknames for 'Morrigan' to see if 'Mog' was one or if Jessica just made it up. Anyway, I accidently pressed on a page about 'The Morrigan', which I think might be some goddess or queen or a mythical (war?) hero from Irish mythology according to the description I barely read. But then it said what the symbol of 'The Morrigan' is, and guess what it was? A CROW!
So there ya have it folks, Morrigan Crow is (sort of) named after 'The Morrigan'.