@reaperthegrim: Flatten the Earth can be interpreted differently. We haven't seen what the wall titans are truly capable of. They can either be multicontinental or a little higher if the statement is to be taken more accurately, such as wiping out civilization of the sort. Also, AT fields can be used offensively and can be put in reverse making an anti AT field. Each angel is capable of causing the third impact since they're all a child of Adam, but that's where I can only see an anti at field being produced. The titan crystal was easily destroyed by the jaw titan mouth meaning it's not entirely indestructible as the AT field.
@valorknight: Well the AT field will prevent them from attacking her head on. If it's capable of tanking a nuke, it's more than capable of stopping a few thousand titans from getting to her. The survey corp have a much better alternative then rounding 10,000 titans which would take a little more than a week, wouldn't you think?