I prefer
Esther Anne Bennett.
I think
Anne would fit very well with your description of her. Mimosa would, in my opinion, be too out of the ordinary, while
Anne makes her a little more soft and...cute. If that makes sense.
Esther Anne Jude. It doesn't sound all that bad, but maybe something is missing... Maybe it's the two short names next to each other. I don't know. If you intend just to use "
Esther Jude" in your story, I'd say it would work out just fine though.
Some other suggestions for a middle name could be
Annabelle,
Nannie or
Maryanne? I think those would go well with both of the last names.
I hope that helped :)