What any country is looking for is proof / evidence that - the person will return after their visit - that the visit is a legitimate tourist visit (or whatever reason they are declaring) - that they will not try to change status after arriving (to settle) On one hand the association with a US citizen might look like a higher risk of changing mind to remain in the US once there - especially as you currently are doing this commute (essentially living in US, but she in Japan). If you (both) write an covering letter 'letter of invitation', explaining the invite and payment of ticket, plus your confirming that your/her normal arrangement is long term, and have no reason to change, that should be fine. Have supporting evidence of commitment / reason to stay with the job in Japan for the foreseeable future should be fine.
And provide your phone No contacts, so that at her interview US embassy can ask you directly if they wish to check. It is the overall impression of not being a risk of trying stay in the US, and wanting to remain in your re-established location in Japan (eg do not want to lose PR status) that will make them happy. Apart from that.. who can tell.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.