A cover per term seems fitting. Remember Michelle Obama had 3 Vogue covers spread over 2 terms as First Lady.
I think, for an American Edition, representation of the current sitting president and first lady are the most important thing to capture. Regardless of what your politics are, it's history. I would even be understanding of 2 covers per VP or First Lady per team, to total 4 covers for 2 terms. Michelle had such a high style profile, so that worked well. Jill is more of a serious figure, I don't see her aligned as an iconic style type of First Lady. With that said, the cover is that much more effective in its clean, American styling. Again, love this cover for her. It's pure.