Hello Kieron, welcome to the forum.
I think you are:
A) Taking Susan's post in the wrong way.
She is just saying in her inimitable clumsy fashion that the "busy fool" may have another income and so he goes and tops it up. His other income could be a pension from a previous job, the dole, benefits or anything really. She just plucked "soldier" and "£300 a week" out of the air to illustrate her point.
She likes to portray herself as a bit of a bruiser but underneath that brusque exterior and Popeye-like attitude to life she stands by her man with a heart of gold and she loves us all!
B) Afghanistan's dangers are are irrelevant to the discussion really.