Mirabelle Ruth gets my vote.
I just really like the sound of it, and you could always use '
Mira' as a nn, so you get to use two names you love. I also like the fact that
Belle is a family name.
Mira would be next choice. It's sweet and simple.
Vivienne I like also, but I know two men with this name, so I always think of it as a male name unfortunately.
Willow is the only one of your names that is not my style. I just find the other three a lot more attractive sounding.
HTH. :)