It seems to be the general view in this thread that Mari a)left Japan for the US straight after Macross and b) did so in the search for more artistic freedom.
I believe it's a bit more complicated than that. For a start Mari had quite a long career in Japan post Macross and ended up marrying an American which I guess contributed to her relocation.
I'm a fan of all her work and have half a dozen non-Macross related albums of hers. Beautiful music, definately a notch above your average pop music, you can tell she's a real artist and a music lover. She gets quite personal in her lyrics sometimes too so her facebook posts aren't really that surprising to me.