Welcome!

If your daughter is already in a Montessori 6-12 environment, then Montessori bilingual should be a strong option, and as far as I know there are only two with established 6-12 programmes in Zurich that could take a year 4...

www.dinsle.ch (you have that one on your list)
and
Rietberg Montessori.

The main decision will be a geographical one. D'Insle is on the seefeld side of the lake, and Rietberg is on the Enge/Wollishofen side.

Always, my recommendation will be to actually visit the school and see how you feel about them, but both Rietberg and d'Insle have a good reputation for being well-established, well-staffed and solid Montessori educational programmes...

If you want more info about Montessori in general / in Zurich, you are welcome to send me a PM and we can talk further. I have three children all in Montessori...