Yeah I couldn't figure out why she woruld be sidelined either. It was a weird plot choice.

Molly- Remember how adamant Charity was that she not get into anything magic? Also if you remember Charity met Michael when he rescued her from some kind of dragon cult. It's entirely possible she was already pregnant. Also yes, her being called as Winter Lady, the care Leah took in training herr prior to that even. And finally- she can use a cell phone. A human wizard, as Harry mentioned several times, cannot do that without destroying it. Plus it would make a great plot point and an interesting arc for Molly.